Single Perfect Tear
From Super-wiki
Dean Winchester displayed an affinity for crying a single perfect tear – see 2.02 Everybody Loves a Clown and 2.17 Heart- and most of Season 4. This is sometimes referred to as the “Single Emo Tear of Manly Angst” or variations thereof. (originated on TWOP)
The term also spread to the writers' room, as evidenced by this quote fromS era Gamble:
Abandon All Hope was the first time I actually cried watching a director’s cut. At first I thought maybe I was just having one of those days, but I checked in with the other writers… I don’t want to incriminate anybody, so I will just say that one or more male producers also shed what we like to refer to as A Single Perfect Man-Tear.
Source (spoilers for s5)