This works best on a very hot day when the balls are hanging real low. While sitting down and wearing shorts, pull out your sack and pin it to the seat with your thumb. The stand up until the slack on your ball bag is taunt. This is when you say out loud, "hey look, I'm stuck in gum" fooling everyone into thinking that you sat in gum. It usually takes people a few seconds of staring at your bag until they realize what it is.
Instead of the predictable Hanging Brain trick, I mixed it up by doing a "Sat in Gum" trick at the bar last night.