Back in high school electronics class I built a "shocker box". Basically a car ignition coil on an oscillating circuit with a spot to attach a wire lead to it. Its been used in a few spots around the shop for entertainment. We had it attached to the steel bolt/nut bins one day. There was a lot of laughter from everyone as they would get zapped, figure out what it was, then watch for the next guy to come by and get zapped.