I wasn't too bad of a kid, but I had a teacher in middle school that I really couldn't stand. His girlfriend had just broken up with him and he'd come to class hung over or after really long sleepless nights and complain about things like not being able to afford his mortgage and birds taking shits on his new truck.
He was the kind of guy that picked up change, so we'd start leaving change in his classroom, glued to desks, on the floor, on his seat, etc, etc. We'd spell out words and (one time) an entire message. He would always scold us but take the change anyway "to teach us a lesson". I must have wasted $20 trying to fuck with his head.
Oh yeah, the locker next to mine was empty and didn't lock, so my locker partner, myself, and some other people in our wing started filling it with garbage. Someone else got busted for it after a janitor saw him try to shove a milk carton in and a ton of rotting garbage spilled out instead. We weren't allowed back to our locker for like, 2 days while the decontaminated everything. Last time I visited the middle school, that locker still smells like shit.
In middle and high school, I would delete random files from people's personal folders that I didn't like, though I was overshadowed by the "troubled" kid that erased the entire student directory at least twice.
I never really got busted for anything in high school, but I was questioned by federal agents after I taught someone how to use IP-Relay and he then used it to send in a bomb threat from our computers class. It was just our luck that when the local police/administrators searched the school, they found a 'weapon and possible explosive device' dumped in a trash can (someone took a stolen exacto knife and an electromagnet out of class and dumped them in a trash can earlier in the day). Pretty shitty.