Stealth games.
I think it was a Splinter Cell game I was playing with a friend that was the most memorable. I was playing co-op, and my friend came up with a very nice plan for sneaking into the building.
Me? I'm one of those "Why just sneak past the guard when I can kill him and stash the body, thus removing a dangerous problem?" type of players. I also like to cram as many corpses as I can into equipment lockers.
My friend walks up to my character, remarking about a surprising lack of guards as he was making his way into the perimeter. About this time, I'm popping open a locker to cram another corpse inside.
I guess I had the timing all wrong, because about 2 dozen corpses cascade to the floor, making a hell of a mess.
My friend won't play that game with me anymore.