People who seem to think that there's some sort of "feud" between you when you actually have no opinion at all.
I always find this bizarre and quite amusing. I love that scene in Grosse Point Blank where John Cusack's character goes to his reunion and this school bully feels they've finally got the chance to settle a "score" from fifteen years earlier whereas Cusack's character has been travelling the world as a professional assassin and entirely forgotten his existence.
I once saw this quite funny site at Uni where, two months after a guy from my course went home with a girl another fancied, the other guy went absolutely overboard in a desperate attempt to pull a girl the guy was talking to, despite the fact the first guy involved wasn't even aware there was a "rivalry" to settle.
I've had this a few times but no really interesting stories to share. But what experiences of this have you had?