OOO! I can answer this one *and* make it about music!!
It's not the nicest thing I was ever involved in, but it was a long time ago, and I was a lot more naive.
In my Jr. High, the band room was *way* out of the way, and not even really attached to the rest of the school. It had huge double doors, and the handles were those u-shaped things side by side. The engineer that designed this part of the school must not have been too bright, as he put the light switch *outside* the room. Some bright young burgeoning delinquent decided that it might be a fun prank to put a bar of wood through the handles (and so, obstructing anyone from leaving), and of course shut off the power. It took a period before anyone noticed.
I am happy to admit that, though I knew about it, I did not mastermind it.