When I was on school I had a friend [girl] since the beginning but after some weeks she just stopped talking to me. I was so pissed that one day I went to school chewing A LOT of bubble gums, and I stuck the bubble gums in the girl's hair. they suspended some boys because of that and no one knew that it was me.
The funny thing about that is that now we're friend again and we're in college together. I never told her about that.
My little sister came in town, when I was staying with my father, (she's the favorite) she pissed me off so bad, that the day she was leaving to go back home, I bleached all her clothes, and put dirt in a couple of her hats... Luckily my father thought it was his fault because he had just washed her clothes 1 hour before that. I was young, and going thru a phase. But now we're the best of friends... and oddly enough no one ever knew it was me.