Dai-Gilgamesh
I used to have a BD who cut out the intercom wires in the band room so we wouldn't get dismissed in the middle of rehearsal. xD Good times, good times. To this day, we still can't hear the announcements.
My middle school bd would take out the battteries of the clock. He for soem reason never told the janitor, so the janitor would come in and see the clock wasnt working and put in new batteries, which my bd would just take out. Once, he replaced it with a drawing of batteries, and another time i paper with a smily face on it.
My high schol bd would just put paper over the clock. Once it was a huge yellow smily face. Another time, it simply said "I dismiss you, not the clock." And then another time "Watch the conductor, because the clock wont tell you the right tempo."