The other variation is to get an old 240v to 12v transformer, get a load of friends to hold hands in a line. The two at the ends of the line hold on to one wire each from the 240v side, whilst you attach the other two wires (the 12v side) to a battery. Nothing happens, until you remove one wire from the battery. Hey presto! Everyone leaps a couple of inches off the floor. Depending on the transformer and the battery you use, will determine
a) how high they jump, and
b) how hard you get punched.
If you really balls-up your combination, it is quite possible that some or all of your friends may well die, but what the hell - if you're prepared to electrocute someone, then they're probably not that close to you anyway.