I say find out where he lives, sneak up late at night, and POOP on his hood. That should cover about $10 work in cleaning it up.
Now everybody's square...
If you don't feel up to that, then take it as a loss and tell everyone he deals with your experience. We are a group. We should be able to trust on another. A heads up is far from a bad thing. It lets others that you trust know who to be wary of.