Back in the old days before homeland security and school metal detectors, we the high school yearbook photographers were given keys so we could get into the school and into the darkroom at night on yearbook deadline periods. For reasons that defy logic, they were master keys to the whole school.
For much of our tenure, we behaved, but I had this idea: our favorite teacher, a writing teacher who shall remain nameless, needed to be pranked. Late one night we got into the school and into her room. We removed all her desks and distributed them evenly throughout the surrounding classrooms, so they appeared to have vanished.
Disclaimer: if anyone is considering legal action in this matter, the statute of limitations has expired.