I dound TWENTY dollars the day before yesterday, but no-one was around so I had no way of finding out whose it was. I kept it, then bought afternoon tea for a friend and myself.
If your friend is the kind of guy who keeps being a pain just for fun, then try this someday: offer to buy drinks or hotdogs or something, then hand over three dollars. Once you've finished eating or drinking, say "By the way, that money used to be yours. You dropped it last week. Thanks!" and see how he reacts.
Alternately, you could do the basic, decent, honest, moralistic thing and give it back. After all, he may have been sent to Earth in human form to test your altruism. You never know...
