When I was in grade school I threw a pair of scissors at a boy. This was after I accidentally scratched a girl on the eyeball with a piece of paper. I was feeling really bad about that and this boy was giving me crap and I didn't want to take it so I threw the scissors. Luckily they hit him with the blunt end and he wasn't hurt, but my teacher was so mad and left me with the impression that I could have killed him. The thing that makes this the worst thing I've done is that at the time I really didn't care how close (I thought) I brought him to death.
I care now, of course.