In middle school, I got in trouble and was sentenced to Saturday school (where you come in for 2 hours on Saturday and do homework in the library). Since it was a hot day and I didn't feel like walking back home right away after, I managed to sneak into the computer lab. At first it was to play games by myself (but basic educational crap like Oregon Trail and Zoombinis).
Suddenly, I remembered that my TA friend gave me the admin password, so I rigged all the computers to have thehamsterdance.com as the home page (well, no longer up... It was 1999 folks, but
here's an almost exact replica), so I opened Task Scheduler to open the browser for the first class of the day (I even rigged one to come on first, and then the rest later), then cranked the volume on every computer, then reseated the mouse and keyboard (with PS/2 connections you'd have to restart the computer for it to work again).
Come Monday morning since my class was across the from the lab and the door was open, I can hear the teacher yelling at one kid for "disrupting the class", then while he was vehemently denying it, the teacher said "Bullshit, Mr. Parrinello's (our VP) office, NOW!!" Then almost a dramatic pause later, one by one the other computers started cranking it, and it went on for a good 5 minutes since he was trying desperately to 3-finger salute the computers, then had to go around one by one to hard restart the computers. The faculty never found out who did it, and it got people humming the song for weeks
.