Balloon trick.( Seen on TV Hustle programme). Bet some adults, or children, that you can walk around for 10 seconds with a balloon on your head. The balloon must not be held on by your hand, someone else's hand or any other device.
When they have tried, and failed, you take out a pin and pop it. Put the deflated balloon on your head and walk around for 10 seconds You have then won your bet.