In a lab we were working in a closed, windowless room. One afternoon, we were doing some silver solder work on vacuum system plumbing. Pranksters decided to heckle us and periodically a hand would reach around the corner and flick off the lights. Naturally we were annoyed because we had to put down the torch to restore the lights. Of course this would wreck our preheat. This was getting annoying. I was not working as an electronic tech at that time, but I still had ties to the electronics lab. From the electronics lab I borrowed an oil filled capacitor and charged it.

Back in our room I connected the capacitor to a little "halo" of wire that guarded the light switch toggle. One had to encounter the halo in order to flip the switch. Since the pranksters were blindly reaching around a corner, they couldn't see the obvious trap. It was interesting because this was really a gang of pranksters and once "bitten" by my little guard, other pranksters were encouraged to join the fun -- omitting the detail about the "bite". They nearly wore me out running upstairs to the electronics lab to recharge the capacitor, but we eventually worked through the entire prankster gang and achieved peace.

It was a 10µF capacitor charged to nearly 1000V. Note that this is quite a punch and it would not be a good idea to have the current path cross the torso. In this case the "sting" was contained entirely in the hand because the switch was enclosed in a metal surface box. As an extra safety factor the extended arm was in contact with a metal door frame.