A prank I was well known in highschool for was having a remote, which worked on all the TV/VCR/DVD combos (as they were all the same model) in the school. In retrospect, it's funny that almost every student in every class I ever had knew I was the culprit, but no teacher ever caught me rewinding, stopping or fast forwarding the movies we had to watch in class.
But speaking of pranks, I'd love an excuse to talk about Leavers Day. The general idea was that on our final day of graduating year, which was the day after the graduation ceremony, any students moving on would play pranks on students and teachers, make a mess and generally muck around.
The year before mine had caused a serious amount of damage (it involved a certain liquid which ruins car paint after a few hours in the sun) and, as such, almost served to ruin it for my own grade when we were warned of a zero-tolerance policy, and the likelihood of the police being informed of any serious misconduct.
It was decided amoung us that it was a tradition, decades old, and impotant to uphold, as long as we were quiet about it. Besides, most of us had been planning pranks for years.
A few that I orchastrated or participated in included putting chilli powder on the toilet entrances (ouch!), stuffing taps with coloured ink soaked felt (such a good feeling seeing students walking around with stained hands), and the tried and true water bomb / flour group sport. There were 2 incidents I could of got in alot of trouble for, the first was stealing witches hats and signs from a nearby road works, which involved the police, and being involved in the concussion of one boy after my friend sprayed him with a fire hose from the second story of the science building (I was too scared to do it myself, lol) but he chose not to press any charges. The only real trouble involved a few boys who damaged the legs of chairs in a few empty class rooms so that they would break, the school actually took them to court. Fair, but it seemed petty at the time.
The best part is knowing that still to this day, the school hasn't managed to put a stop to it!