People who ask for dumb stuff as a joke at the counter in fast food restaurant.
When I ask, "Anything else?", and someone says "A million dollars", it's not funny. It pisses me off, wastes my time, and makes me want to rip their dumbass head off their shoulders and beat their lifeless corpse with it.
You know what. Most things people do when they walk through the door at work piss me off.