It's Scott Alexander's cards across routine!
This is a cards across where the spectators do all the work. Ten cards are dealt out by a spectator. He then seals them in an envelope and hides them in a "safe location." Just like a smuggler, he hides them in his pants. You assure him that there is no way you would be able to extract the cards now.
He then takes ten more cards and goes into the audience to have three of them selected. He seals these ten in an envelope himself, which is given to another spectator who hides them in his pants too. Again you emphasize that you never touch the cards, even during the selection process! Then the three selected cards, and ONLY the three selected cards take a hilarious flight from Guy #1's envelope to Guy #2's. This is an easy to do, outrageously fun, eleven minutes worth of solid comedy magic! You can play this jokes as cheeky or as innocent as you want. Customize the presentation to play for kids by putting the cards under their hats, or in the guys pants for the rowdiest adults. The presentational choices are limitless. Yet, the method is so easy to master yet so diabolically clever you won't believe how much milage you can get from just this one routine.