If you're looking for some good, clean—albeit semi-reckless—fun, you can't beat taking some household items and assembling them into a combustion-based ping-pong ball gun.
If you've ever built a spud gun, the PVC pipe constructions that help launch unlucky potatoes into the stratosphere, you'll be more than familiar with the design of the ping-pong pistol. All you need is a paper towel tube, duct tape, hair spray, a utility lighter and a ready supply of ping-pong balls. If you're feeling particularly industrious you can upgrade the paper towel to a sturdier material, but the paper towel tube should last at least long enough for a more responsible friend to insist you put it down before someone gets hurt.
As always, exercise good caution and judgment but most importantly don't come crying to us when you burn the hair off your arm. If you have your own fun backyard tricks involving fire or otherwise, sound off in the comments.
How to Make a Ping-Pong Pistol [Dangerously Fun]