What was the worst trouble you've ever been in at school?
Or what was the most insane thing you've ever gotten away with in school?

This one is simple. While I was in a computer class at school I created a text document, typed "start new.bat" ten times on it, and renamed it "new.bat"
Anybody who's ever done this simple trick before knows what it does... The file opens up ten copies of itself, then each of the ten copies will open up ten copies of themselves, etc.
I then used the NVIDIA manager to start it when I hit ctrl+alt+shift+8.
Due to a little incident involving several proxy programs and such, the network administrator had block everything except for AutoCAD on the computers. The hole in the computer's security was that NVIDIA started up with the computers and the settings menu can be accessed through an icon in the taskbar's notification area and the file blocks could be overridden with hotkeys.
About a week after I created the file the network administrator started checking people's computers with VNC to make sure they weren't doing anything they weren't supposed to. When he accessed my computer I hit the hotkey to start the self-opening program and then turned the computer off. I turned it back on, logged back in, and did the same thing the second time he accessed my computer.
The third time I spammed the living crap out of the hotkey and opened about a hundred of the program and waited for my computer to completely lock up before restarting it. After that he came into the classroom and accused "whoever was at computer #9" of trying to crash the network. Casually, I told him that I was on the other side of the room discussing my friend's graduation party with him while watching the movie that was playing (it was one of the last days of the year, we had a free day).

I'll wait for a few people to post some of their great exploits before posting about the grilled cheese incident and the carrot prank gone horribly wrong.