I never really did anything THAT bad. I was a total little shit to people in primary school though, and smacked some guy's head off a wall for a quite trivial reason.
Smashed the odd pane of glass in secondary, twice from snowball fights. Hit a teacher in the face with a snowball after it missed my friend, because he moved, because the door right next to him opened, which enabled the 'ball to enter said door, narrowly missing the opener, sail into the corridor and hit a teacher's face far better than ANYTHING I could have done on purpose. Of course I was caught because of my hysterical laughter taking up 110% of my breathing capability rendering me unable to run away, or even stay conscious nearly. Intentionally threw a snowball at a fairly strict teacher's umbrella after he turned around after he gave a lot of us a row for throwing them. WTF did he expect!?
Following a home economics class, me, three friends and our foil-boxed macaroni meals kicked them about a corridor, penalty-shot style, then kicking the mess up the wall!
We ran away like poofs straight away after we did it though!
In college I got a fairly serious slap on the wrist for putting a pic of some gothy black T-shirt with "JESUS IS A CUNT" as the desktop several times. Someone else started it and kept re-doing it, I found it immaturely hilarious, so it kept on setting it back as well, then one day a tech caught me right in the act and of course I couldn't even TRY to say that other folk had been doing it too. I also got caught looking at porn once, but the shade of red my face went was proof enough that I was never gonna do it again. I didn't, either!
;)