This term is usually associated with online
games. The term is used in the event a player describes a situation in which the outcome was unbelievable, unlikely, or
amazing. Player(A) then describes the event to his friend, player(B), who was not there to
witness the event, which to him sounds unbelievable. In which case, player(B)in disbelief says, "Screenshots or it didn't happen."
Player(A): LOLWTFOMG!
11!!cos(0)
1!!!! HAHAHAHAH, I just one shotted a paladin through his
nub shield.
Player(B): Screenshots or it didn't happen!
Player(A): HAHAHLOLOMGWTF!!1!!!cos(0)!1!! I just
shot my tube from The Hotel across the map and killed player(C) at the Gatehouse on Karkand in BF2 without knowing where he was.
Player(B): Screenshots or it didn't happen!
Player(A): Here you
go, lol pwnd.
Player(C): NO WAI!!