Every so often you find yourself in possession of fake money. Counterfeit bills that have no real value, but you got them as change, or found them on the ground, doesn't really matter how you got them as now you need to get rid of them. Now even if your money is fake, you should still get something for it.
One good place to take your bad money is charity. Teach a lesson to the man asking for donations outside of the store, just imagine him explaining this to his boss. Church collection plates are another fine opinion, and give you the opportunity to exchange your problem for actual money. Put that fake ten in the plate, and reach in and grab a two fives as "change". The church isn't selling a real product, why should they get real money? The best part of the charity option is you can write it off on your taxes.
Another good option is to spend it. Now you can't do this at any retailer, you need to find a small street vender, or any place with bad lighting. The man selling hot dogs on the street isn't going to check. A stripper doesn't have time to check every bill that is placed in her thong. Kids with a lemonade stand have never even heard of counterfeit money. Have a bad waiter? I got a great way to leave them a tip.
It might be fake, but it is your money. You didn't create it, you just stumbled across it. You could do the right thing and destroy it, or you could have a little fun.