A tradition, at least in the high schools in my area. High school seniors band together to plan low-level mischief as graduation day nears. Sort of a nose-thumbing at the administration after four years of imprisonment.
Most senior pranks are fairly harmless, just meant to disrupt the school day a little, though some can get out of hand. I remember the school lawn being filled with hundreds of "for sale" signs, thousands of crickets loosed in the halls, buying a stripper for the principal, and writing "Class of 1998" with soap on the windshield of every car in the lot.
My senior prank had a technological twist. Most high school PA systems differ from a home stereo system in that the speakers are all powered from one single cable in a giant loop, instead of having one cable from the amp to each speaker like in a home system. Usually the signal is created in the main office and sent on down the line to all of the speakers in the hallways and classrooms of the whole building. There is no reason however, why the signal (sound) needs to come from the beginning of the line, or even the end. You see where I'm going with this .
One late night after drama club rehearsel, me and a pair of wire clippers made our way into a little used room in a far corner of the school. Two snips and the old PA speaker had been liberated from its previously mundane life. A little bit of wire twisted and spliced on here and run up into the ceiling tiles. Be careful if you try this, even when off these wires have 24 to 70 volts DC on them... it won't hurt you but you will jump.
I fished the wire through the ceiling and out down to an empty cabinet in the corner of the room. A cheap K-Mart boom box out of my backpack was my new signal source, with its speaker wires now twisted around those dangling from the ceiling. Purists would say I'm crossing an 8 ohm system with a 70 volt, but high quality wasn't excactly my goal here..
Come Senior's Last Day, I dropped in a cassette, hit the play button and melted back into the concealing throng that is high school. A few minutes later, well, use your imagination