Everyone loves a nickname, and Supernatural has plenty for the characters, the actors, and of course the fans ourselves.
When Supernatural started, SN was used as an abbreviation for the show on things such as Livejournal community names, for example the original sn_newsletter. However some fans found it could be confused with the TV show and fandom for "Sports Night", while SNL was associated with Saturday Night Live.
So SPN became the commonly used abbreviation. Its usage spread even more widely with the advent of the letter economical Twitter.
SPN (pronounced "ess pee en") is usually capitalised and is used to refer to the show and the fandom.
Sam and Dean
While not exactly a nickname, the most common term used to refer to Sam and Dean by fans, and occasionally by Bobby, is 'the boys'.
Sam and Dean have a ritual where Dean calls Sam a "Bitch" and Sam responds with "Jerk". While this is strongly associated with the characters, it has only been referenced three times on the show.. (video compilation of references).
Most commonly it is the Winchester's adversaries who refer to them by a variety of pejorative epithets:
- Uriel refers to Dean, and all humans, as 'mud monkeys' 
- Atropos, Crowley and finally Castiel himself, refer to Sam and Dean as Cas' 'pets'. 
- Interestingly, Sam is called Chachi by Gordon . and Dean by Pamela. This is a reference to Chachi from "Happy Days" and "Joanie Loves Chachi".
Probably the most expressive term is used by the ever articulate Crowley who calls them "denim-wrapped nightmares". . He also calls them the Hardy Boys, a term long-used in the Television Without Pity recaps of Supernatural. That forum also referred to the boys in 2005/06 as The Brothers Dean. This related to Jared's previous role as Dean Forrester on Gilmore Girls. Occasionally Sam was referred to as Cute!Dean and Dean as Hot!Dean.
Crowley also calls Sam "Moose" and Dean "Squirrel", referring to the cartoon duo of Bullwinkle (the moose) and Rocky (a squirrel) and Timon and Pumbaa who are a cartoon meerkat and warthog duo who first appeared in Disney's 1994 animated film The Lion King. Crowley's caller id for Dean is Not Moose. 
Dean: House rules, Sammy. Driver picks the music, shotgun shuts his cakehole.
Sam: You know, Sammy is a chubby 12 year old. It's Sam, okay?
– , 1.01 Pilot
Dean's nickname for Sam is Sammy, generally used either for teasing or in moments of great emotion. While Sam initially protests its use after he and Dean first reunite in 2005, it becomes clear it has as much meaning for Sam as it does for Dean when Gordon Walker uses it and Sam retorts "He's the only one who gets to call me that.". For a count of every time Dean uses this nickname see Sammy.
Most of the nicknames for Sam both in canon and fandom refer to Sam's Height:
Crowley in particular has a number of nicknames based on Sam's height including:
Rowena refers to him as "Giant" in 10.19 The Werther Project</ref>
In 8.02 What's Up, Tiger Mommy? Crowley calls Sam "Samantha", possibly a reference to his long hair in Season 8.
There are also nicknames for the various incarnations of Sam:
- Evil!Sam - the name given by fans to Sam when he was possessed by the Meg!Demon . Over time the term has come to have a broader use, especially in fanfiction where there is a whole genre based on the premise of Sam, for some reason, becoming evil.
- RoboSam - used by Dean to describe Sam when he didn't have a soul.  and was widely used by fans and TV reviewers. Other terms used included Soulless!Sam or Not!Sam. Sam with a soul was occasionally referred to as soulful Sam and Care Bear Sam Source.
- Samifer - used by fandom to describe when Sam is Lucifer's vessel.
- Sampala - used by fandom to describe when Sam is transformed into the Impala by Gabriel.
Dean doesn't really have a nickname. Sam calls him Dean. A lot.
Occasionally others use terms that refer to his good looks: Ghostfacer Ed Zeddmore calls him "chisel chest" , and Brandon a waiter at Biggerson's Restaurant refers to him as "Ken Doll" as he serves him a turducken slammer.
In 7.11 Adventures in Babysitting Frank Devereaux gives Dean a variety of nicknames; Sweetie pops; Buster Brown; My Little Lamb; Tarzan; Grasshopper; Cupcake. Frank also compares the two of them to Cheech and Ed from Ma Bell while they are costumed as electricians while undertaking surveillance.
Alastair: Now we're getting somewhere. Holy water? Come on. Grasshopper, you're gonna have to get creative to impress me.
Gabriel and Cole are known for calling him "Dean-o".
Dean (referring to the Impala): Woah!! Listen to her purr! Have you ever heard anything so sweet?
Sam: You know, if you two want to get a room, just let me know, Dean.Dean: Don't listen to him, baby. He doesn't understand us.
– , 2.03 Bloodlust
Dean's term of endearment for his beloved car Impala is 'baby'.
It is common for fans to have characters refer to the car as "the Impala" in fan fiction, but it wasn't until 2.01 In My Time of Dying that she was called thus on the Show (by Sam). Most notably she's called the Impala in the monologue by Chuck in 5.22 Swan Song.
The nickname Metallicar originated on Television Without Pity on October 11, 2005 source. It was coined because Dean enjoys listening to classic rock music like Black Sabbath, Led Zeppelin and, of course, Metallica while driving. It became commonplace throughout fandom, and has appeared on merchandise.
Cas is a nickname for Castiel, first used by Dean in  and later commonly by other characters. Before its use in canon there were relatively few instances of this diminutive in fandom, and when it did appear it was generally pilloried. Subsequently its use became widespread.
The show's writers spell the nickname "Cass" (example), and it also appears that way in Tie-in novels. It is spelled Cass in the Season 7 promo. In fandom, and particularly in Fanfiction, it is almost exclusively spelled "Cas".
The demon Meg refers to Castiel as Clarence in a reference to the angel in the movie It's a Wonderful Life . In 9.03 I'm No Angel, Castiel adopts the name Clarence as a cover when he is human.
Fannish nicknames for Castiel include:
- Godstiel - after he has absorbed the souls of Purgatory and proclaimed himself a god. 
- Thingstiel - Castiel in his true form
- Clairestiel is the mashup nickname for Castiel while possessing Claire Novak as a vessel.
When Genevieve Padalecki (then Cortese) was cast as Ruby in Season 4, her version of the character became known as Ruby 2.0, New Ruby or its contraction Nuby. Katie Cassidy's Ruby became known as Old Ruby.
The demon Casey reveals that Azazel is the true name of the demon the Winchesters have been hunting in Season Three. In Season 1, he is referred to as "the thing that killed Mom and Jess" and subsequently, after John reveals he knows what it is, as The Demon.
In Season 2, Dean refers to him as The Yellow-Eyed Demon. Fannish shorthand for this was YED.
Another fannish term was Celine Demon coined on the TWOP boards on September 14, 2005, and derived from a misreading of the words Ceiling Demon as Celine Dion
- John Winchester : By fans as Papa Winchester and on TWOP - as the Lying Liar That Lies. Reviewers at TV Guide have been calling John Winchester "Big Daddy Winchester" since Season 1 Source.
- Lucifer: Gabriel called him "Luci" in 5.19 Hammer of the Gods and he is often referred to as such by fans too. He is called Samifer when possessing Sam. Hallucifer is a fan-created nickname for Sam's hallucinations of Lucifer which originated in the LJ community ontd_spnparty's 7x01 Party Post. source
- Gabester - mashup nickname coined after the Trickster was revealed as the archangel Gabriel .
- Sampa: Term coined by fandom in early Season 6 for Samuel Campbell to distinguish him from Sam.
- Victor Henriksen - who needed a nickname because no-one could spell his real name - dubbed "Agent Scooter Javert Bad Assitude" on Television Without Pity
- Abaddon - dubbed by Crowley as "the world's angriest ginger". 
Cast and Crew Nicknames
Well obviously we both call each other J, and when anybody says "Alright J, they're ready for you", they generally get both of us. (Points to Jared) J-Rod. I call him J-Rod. The crew, he gets J-Rod. And then I get Jackles. Yeah J-Rod and Jackles are probably the two most commonly used.
The most popular fannish terms are J2 or J-squared. The term "J-squared" was used by Misha in the episode 6.15 The French Mistake. Jared and Jensen are also referred to as "the boys" by both fans and fellow cast and crew. The portmanteau "Padackles" was popular in the first couple of seasons of the show.
In a January 2007 issue of Pop Star magazine, it reported that Smeckles was Jared's nickname for Jensen. At EyeCon April 2008 Jared listed some nicknames for Jensen, including Smackles and Ugly, and mentioned Stretch for himself. (Video)
In fandom, Jared often attracts many of the same nicknames as Sam, which is not surprising given they are the same height. Moose became popular after its use in the show and at conventions, and especially following Jared joining Twitter. Puppy is another commonly fannish nickname, referring to Jared's boundless energy, affectionate nature and good humour.Also J-Pad.
Adding the prefix "Pada" to anything is a common fannish habit: Padacock is a fannish nickname for Jared's penis, while his and Genevieve's first child Thomaswas referred to as the Padabump and as mini-Moose after he was born. The on-set logistics around the impending birth were known as "Operation Moose Drop"
Frackles is a fannish nickname for Jensen's freckles, and he is called Jackles by some crew members.
- J2 be used in combination with other actors eg J2M refers to Jared, Jensen and Misha, J2M2 refers to Jared, Jensen, Misha and Mark Sheppard.
- "Sir" is the nickname for Jeffrey Dean Morgan in the ONTD community - ontd_spnparty as well as CAPSLOCK SPN. Sir is always on topic.
- Misha on Twitter is known as the Overlord. Other nicknames also include Mish Mish.
- Richard Speight Jr.: Pepsi Angel was nickname used to refer to Richard Speight Jr.that arose (probably first at Facebook) from Richard's Pepsi Max commercials, and after his appearance at Salute to Supernatural Chicago 2010, where he was completely dressed in Pepsi Max clothes.
- Mark Pellegrino: Marksha - an nickname of complex origins from Mishaland a CAPSLOCK COMMUNITY.
- Chad Michael Murray: Mayhem - a nickname arising from RPS fanfic.
- Eric Kripke was generally referred to by fans as Kripke, or occasionally The Kripkeeper or Kripmeister.
- Disappointingly, fans have failed to refer to Jeremy Carver as "The Carver"
- According to the Supernatural: Official Magazine Issue #18 writing team Andrew Dabb and Daniel Loflin were dubbed "Dandrew" when they joined the writer's room.
- Location manager Russ Hamilton is known as "Movie God"
- 1st Assistant Director Kevin Parks is known as Parksapedia because of his encyclopedia knowledge of everything Supernatural.
- 1st Assistant Director Johnny MacCarthy is known as Johnny Mac.
When the Supernatural fandom began, fans would occasionally discuss collective terms that could be applied to Supernatural fans, similar to "Trekkies or Trekkers" for Star Trek fans, or "Whovians" for fans of the Doctor Who. Discussions were had, polls conducted, suggestions such as rocksalters, saltgunners, renegades and roadies canvassed, but nothing ever stuck.
Super fans has been used occasionally - possibly coined by TV Guide reviewer Matt Roush is response to a fan postcard campaign in February 2007 source. In the show Becky Rosen is referred to more than once as Sam's "super fan" 
Around early 2011, the term "Supernatural Family" came into circulation, used at first by Jared to describe how he felt about the relationship between the cast, crew and fans: "It's like my third family," he says of his fans. "I have my family, my on-set family, and then our 'Supernatural' family, so I love them. My 'Supernatural' family's the biggest and strongest, so I love 'em." . He also used it at the Comic Con 2011  The usage spread amongst other crew members on Twitter such as Jim Michaels.
For the 2013 People's Choice Awards, there was also a new category for "Favorite TV Fan Following". The Supernatural fandom was referred to as "Dean Girls, Sam Girls, and Misha Wives". Within hours of the polls opening, fan complaints about this led to it being changed to SPN Family. We won the award!
Although not widely used, Jensen fans are sometimes called (usually by themselves) Ackleholics, and Jared fans are Padafans or Padaphiles.
Fans of Divine: The Series have been dubbed Divinites.
Of course most fans have individual online 'nicknames' or handles that we use on the social media site, message board or websites we are involved with.
Anyway, I'll think of you as friends not followers. But then again, maybe minions is a better term... I'll percolate.
– @mishacollins 2:07 PM May 13th 2009, Twitter
Misha started the tradition in Supernatural fandom of the Twitter followers of particularly cast or crew being granted a particular name. The following are those currently in use:
- Misha's Minions. In the meta episode 6.15 The French Mistake, Misha calls them MishAmigos.
- Jared's Moosekateers
- Jim Beaver's Twidjits
- Jim Michaels' Jimions
- Russ Hamilton's Russticles
- Mark Sheppard's followers are known as Bob, so dubbed by Mark source.
- Traci Dinwiddie's T~bugs
- Matt Cohen's Coheners
- Colin Ford's Colinites
- Kim Rhodes's Rhodies
- Tara Larsen's Larsenists
- Sebastian Roche's Acolytes
- Richard Speight Jr.'s Twicksters
- Rob Benedict - Chuck's chicks or Rob's Roadies
- Todd Stashwick's DracPac
- Chad Lindberg's Chadlings & Badasses
- Clif Kosterman occasionally used Duckers after the rise of Duck Nation, since 2013 uses Clifhangers
- Gabriel Tigerman - Gabe's babes
- Rick Worthy's Betas
- Mark Pellegrino - Lucifer's legionnaires
- Ivan Hayden's Resistors
- Todd Aronauer's Aronauts
- Divine: The Series Divinites
- DJ Quall's Garth Vaders
- Alaina Huffman's Ginger Knights
- Travis Aaron Wades's Wadestars
The Supernatural Wiki began life as a website called Super Canon in early 2006. When it transformed into the wiki format in August 2006, the name Supernatural Wiki was our new official name. But the nickname Super Wiki soon stuck and became widely used, especially when we adopted it as our Twitter handle in late 2008.
- 1.01 Pilot
- 2.10 Hunted
- 2.20 What Is and What Should Never Be
- 4.07 It's the Great Pumpkin, Sam Winchester
- 6.17 My Heart Will Go On
- 6.20 The Man Who Would Be King
- 7.01 Meet the New Boss
- 2.03 Bloodlust
- 4.15 Death Takes a Holiday
- 5.10 Abandon All Hope...
- 8.02 What's Up, Tiger Mommy?
- 8.17 Goodbye Stranger
- [[9.16 Blade Runners
- 5.13 The Song Remains the Same
- 10.15 The Things They Carried
- 6.21 Let It Bleed
- 2.14 Born Under a Bad Sign
- 6.07 Family Matters
- 5.08 Changing Channels
- Buddy TV set interviews Sept 2008
- 3.13 Ghostfacers
- 4.04 Metamorphosis
- 6.10 Caged Heat
- 7.17 The Born-Again Identity
- 8.17 Goodbye Stranger
- 6.22 The Man Who Knew Too Much
- 3.04 Sin City
- 9.10 Road Trip
- 5.01 Sympathy for the Devil
- 7.08 Season Seven, Time for a Wedding!
- Jared interview with Zap2It
- Nerd HQ session