My stepdad got a rep in high school as a psycho after a number of incidents involving bullies (bear in mind this was back in the seventies...). The one that comes to mind is a jock who basically threatened to beat his ass to take his food, so my stepdad (who was pretty small at the time) feigned acquiescence, then as soon as the dude's back was turned, clubbed the dude over the back of the head with his heaviest text book hard enough to knock him unconscious...