Vayne is cursed!
So, I'm usually a pretty chill guy, maining supp and playing mostly mages (I might occasionally rage if enemies are being @$$3$ or if a teammate does something monumentally idiotic, like picking Rengar top against a Rammus), but rarely, I'll play Vayne. Whenever I play her I seem to get more annoyed at my own mistakes and other people's mistakes, more tense about the whole game etc.
So maybe the Vayne mains were actually nice people before she was released or they started maining her.