Now this is a funny prank that you can pull on children or some of your more gullible friends. All you do is demonstrate for them that you can stick a funnel in the front of your pants and a coin on your chin, wait ten seconds, then dump the coin into the funnel. When they try to do it, you sneak up in front of them and dump water into the funnel. They'll look like the totally pissed themselves, and then probably try their best to beat you to death with the funnel. Great trick.
Note: don't use a metal funnel.