What's Your Pet Peeve?
I'll tell you mine. It's when people obliviously block an entrance or an exit, selfishly standing there without any sign of future motion, when it would be obvious even to a sight-impaired gnat that that streams of others are desperately trying to get in or out. This behavior is not only scarily dangerous, it's incredibly piggish and obstinate, and I always fantasize about shoving these oafs to the ground and breezing over their bodies--but they're generally very large.
Runner up: People who perversely push "Close" in an elevator when they see that you're coming for it.
Second runner up: People who glance around the room for someone better as they're talking to you.