Online multiplayer FPS fans. I have to listen to one of these twits Mon-Fri every week because we're both required to show up at the same place at the same time and EvErY gOdDaMn DaY he and all his friends are clustered around, talking about whatever FPS came out most recently, talking about what kind of cheesy tactics pissed them off at 1 am last night and how they're sick of playing against kids all the time. I can tune out most of them, but this one twit, you could make out his voice from across a metal concert, it's so annoying.
My hatred is irrational because everyone has the right to play any game they want (except for kids, they're not allowed to play God of War for some reason . . . god forbid they learn some puzzle-solving skills). I yak with my friends all the time about whatever fighting/RPG/adventure game I got recently, but usually I have the decency to do it in my own home, not right behind someone's head while they're trying to do something else.