Payback for an annoying and nasty flat mate?

I've lived in student accomodation at uni with four other people for a year. 3 were lovely but there was one guy who made our lives a living hell. He stole at least �50 worth of food off me over the year, messed up the kitchen so badly we had a fly infestation, used or stole all of ours things (once I didn't even have any forks to eat with!) made constant noise, and insulted us. We contacted the administration but they did nothing. Everyone else has gone home for the holidays now, and it's only me and him left in the flat. I wanna do something to get revenge, but I have no any what. Any suggestions? :P