Ping-pong thrower
Homemade flame thrower
Fireballs
Homemade snickers bar
Bread
Pencil crossbow
Tilt-shift photography
Duct tape projects
Build with Grid Beam
Free Props
Make Cheap Whiskey Taste Like Fancy Whiskey
Ginger Beer
Relight a candle via its vapor trail
Flammable gas in a glass jar
Decomposition of mercury(II) thiocyanate
Polymerization of nitro aniline
Turn water into ice in a few seconds by freezing distilled water for 2.5 hours in a bottle, and then hitting the bottle
Make a homopolar motor with just a battery, a wire, and a magnet
Measure speed of radio waves: Put the chocolate bar (or a piece of cheese) in the microwave and switch the power off as soon as melting begins. The bar melts at regularly spaced spots, half a wavelength apart.
Rubbing a plastic spoon with a piece of wool charges it. Such a charged spoon can be used to extract pepper from a salt–pepper mixture by holding the spoon over the mixture.
Measure weight of a car with a rules (measure area of contact of tires and multiple by tire pressure)
Show that light is a wave with your fingers only — two fingers in front of your eye, almost touch, see black lines

Next time you see a "How is my driving?" sticker on a car or truck, and the driver did something worth complimenting, call and compliment the driver
Walk into an office building and ask to see the elevator inspection certificate
Call the NYC Department of Health and ask what the health code violations were for a restaurant of your choice. (An "A" rating means a restaurant could still have had 13 violations)
Read an End User License Agreement. In its entirety
Next time you see a movie that, in the credits, says that no animals were harmed, verify it (not sure how)