A few years ago now I discovered that my school had installed a VNC program on every computer in the school. The student accounts had lots of restrictions put on them so I shouldn't have been able to navigate to the local hard disk and run the viewer program but, for some reason, they did not prevent me from creating a Windows batch file and navigating my way to the VNC viewer program via command prompt.

By fluke I managed to guess the password that allowed me to type in the IP address of any computer connected to the school network and control it remotely. Each computer had it's IP address written on a sticker stuck to it. Needless to say plenty of pranking was achieved until I got caught.

I accidentally pranked myself at my state examination, where we had do do a small presentation about our thesis (ppt projected to the wall). On the notebook, autorun was enabled, and the speakers were on. When I plugged my pen-drive in, a "teen and two black cocks" video with full volume started (I don't know how it got there :P), I shouted "fuck it", and since there was only touch pad, which I'm not used to+very high mouse sensitivity was set (and panic of course) it took me 5 seconds to shut it off. I was lucky, that it happened at the beginning, so there was only 2 or 3 professors in the room.

So it should be repeated somehow with on of your friends/enemies.