You all remember the game Operation right? If you don't then shame on you as it was only the greatest kids game EVER!!!
Even as an adult it's still fun to play but these guys didn't think it was quite fun enough, so they decided to inject their own sinister twist. They set about rigging the board up to a paintball gun which was aimed at the players ass. You can probably guess what happens when he fails to operate correctly, right? Yup, instead of a simple buzz from the board, he gets a big old paint shot to the buttocks. Ouch!
Good idea for the stag do though!