This one complete Psycho in my school once bit my arm for about 5 seconds, just because I touched his iPod to look at what he was playing (I had one of the ear phones on. Therefore, he couldn't really say i was being nosy).
Also from the same guy: Whipping everyone with his earphones (really painful), stapling the back of my hand about 4 times (followed by the back of my head), and just generally being really sadistic. He worries me.