Having a laugh is what a stag do is all about. If that happens to be at the expense of the stag, well, that'd be a real shame!
The 'Jason Bourne' stag prank
This is a classic stag do idea but so rarely executed with finesse (see the video in the stag do pranks video archive of a belting effort). So, the concept is simple, kidnap the stag from his house in a dawn raid. 'Cuff him and blindfold him and then drop him in the middle of a field without any money or method of communication. If that field happens to be in a foreign country, so much the better. If you leave him with a video camera (flip etc) he'll be able to record just how miserable he was when you left him alone!