When younger, Sam and Dean had a ritual where Dean called Sam a "bitch" and Sam responded with "jerk."
In an earlier version of the script for the 1.01 Pilot, the exchange was written as Bitch and Prick!
While this is strongly associated with the characters, it has only been referenced seven times on the show:
The first instance of the exchange between Sam and Dean, which takes place in their father's vacant motel room after their argument on the bridge.
After Gordon kidnaps Dean and nearly kills Sam, and is subsequently arrested, Sam and Dean say it in the Impala.
2.20 What Is and What Should Never Be
When in the Impala with wish-verse Sam, Dean calls him a "bitch". Sam's response is "what are you calling me a bitch for?"
A "Bitch-Jerk" exchange occurs between Crowley and Dean, signifying his demonic lack of care for Sam and his newfound relationship with Crowley.
10.05 Fan Fiction
When Marie playfully calls Dean a "jerk" and tells him to take the Samulet she made for the Supernatural musical, out of habit Dean responds to her with "bitch," then quickly realizes what had just happened and the weighted gender implications of the comment, but Marie, Supernatural fan that she is, recognizes the reference and laughs it off .
As they are about to go to sleep in the Impala Sam says, "Goodnight Jerk" and Dean says, "'Night Bitch."
12.22 Who We Are
Before Sam heads off to lead an attack on the British Men of Letters while Dean stays behind to help Mary, the boys hug and then part with the affectionate exchange.