The most trouble I got into wasn't at school, but at college when I sent a rather, let's say inappropriate e-mail to my old headmaster at my old secondary school. I found his picture on the school's website, cut his head out and pasted it around a PowerPoint slide, and wrote in massive letters that he 'does inappropriate things' to horses, and animated his head to bob left and right to some stock music. Stupidly, I used my college e-mail account *facepalm*, so they simply traced it back and I got a very stern, very loud telling-off from the vice principal.
EDIT : Just remembered that in secondary school, I got into a small bit of trouble for saying a substitute teachers face looked like a pancake.