Walking and people that make walking a general pain: Trying to maneuver you way into a classroom when someone is walking on the LEFT side of the hall (their left, that is!
) and is coming right at you. People that enter a building using the LEFT door, which, as everyone knows, is meant strictly for exiting. People that walk into an elevator the instant the door opens, no matter if four people are disembarking. That kind of thing...