In a gym?
Here's my number one: When some douche interrupts you so you can do upright rows over his chest, aka spot his massive 225 bench that he can't seem to do. This prick couldn't get one, and he was like "Keep going". Guess what folks, if you don't have a training partner, don't ask other people for spots.
Number two: Stolen from Croatch - the Prick that does his reps infront of the fucking dumbbell rack. Thanks tough guy. I hope you do rows next, and actually rest on the rack.