This often rage-inducing saying is typically preceded by a blatantly honest statement that's likely to insult at least one person with it's cold, bitter truth. Frequent usage of this saying can spread it's use like a highly aggressive plague, eventually saturating almost all conversations, particularly on the Internet where anonymity encourages impolite truths.
Erin: Dude, this game is mad hard.
Jay: If you just had a lobotomy it might be. Just sayin'.
Erin: ... I hate you so much right now.
Jay: Look, I'm just sayin' that-
Erin: DIE IN A FIRE!