kengr

Old practical joke in some industries/labs:

A box with a power cord and a switch that is labeled "do not turn on". If plugged in and turned on, it'd trip the breakers and shut down the whole room.

My variant, that I had the idea for *decades* ago, but would get you in *so* much trouble if you built it now:

A box with a large buttom and two plastic panels. One is illuminated and says "Press and HOLD to activate"

If you do, that panel goes out and the other lights up "Release to detonate"

(rigged with a firecracker equivalent that goes bang if you do)