Hold your friend hostage and tell that mother fucker that if you don't get your 30 bucks back then his sister will be hanging out at the bottom of the nearest large body of water.
sounds like a waste of time to me. either confront him(which doesn't have to end in a fight) or let it go. your saran wrap is very childish as a pay back for getting ripped off.
Let by-gones be by-gones bro, i was in your place before and no amount of physical intervention will guarantee you money back chock it up as a loss and be more weary when picking up next time. Catch em' in the act next time instead of handing over the money.