Inflammable means flammable? What a country!
That ALWAYS bothered me! It just doesn't make sense!
Making thermite is pretty cool, and probably illegal in several states. Of course, explosions in general are pretty cool. And illegal in several states.
These are mostly pranks as opposed to experiments, and they may have been mentioned already.
If someone is annoying you and you want them to be distastefully preoccupied, try this (you'll need access to some chemicals): slip some magnesium citrate into their drink. Magnesium citrate is a very strong laxative. Should put them in the bathroom for quite some time.
If you've got some friends around, you could do everyone's favorite science thingy: Egg Drop! Use household materials to build small contraptions that will contain an egg and prevent it from breaking after being dropped from a certain height. I think there's a thread on this forum with some ideas for designs; pretty sure it was the thread for the Egg Drop strip. Hey, try using the Non-Newtonian fluid mentioned earlier in the thread!
Liquid Nitrogen kicks ass in all categories. Get some and have fun. Try soaking a hollow rubber ball in it, and then dropping it on the ground. Should break as easily as glass.
Make a pressure-powered potato cannon out of PVC pipe. It makes a loud noise when it fires though, and a few seconds later makes a deep, loud trumpet noise. My friend did this, and we wasted 20 potatos firing the thing. SO fun.
If you don't have any nice supplies, but have some very basic materials, try pouring nail polish remover into a styrofoam cup. It's a low-strength acid, so it will slowly dissolve the cup into a puddle.
There is a chemical (I don't know what it's called, the person who told me about this refused to tell me the chemical because of its effects) that will turn urine blue, but is otherwise harmless. There is also a serious medical condition that you know you have if your urine is blue, though the chemical has nothing to do with it. This is a bit of a severe prank, if you do this to someone else you should tell them you did it after they freak out, or they will end up in the hospital spending lots of money getting tests done to see if anything is wrong. The other option is to do it to yourself so that you can have blue urine for a little while, which would be pretty funny.
Coke and Mentos! There is an easy way to convert this trick into a prank. You'll need a two-liter bottle of coke, one Mentos, a drill with a drillbit slightly wider than a piece of string, a piece of string (preferably 3 inches or longer), and scissors.
--> Use the drill to drill a hole through the Mentos. Be careful that you don't split it in half.
--> Thread the string through the hole in the Mentos.
--> Open the bottle of coke. Drink/pour out a bit of the liquid so it is not so high in the bottle; if it's too high, this may end badly for you. Hold the Mentos over the opening, with the ends of the string sticking out on either side.
--> Screw the cap back onto the bottle with the Mentos still there. It should go over the Mentos and part of the string, causing the Mentos to be held in place above the liquid.
--> Cut off the ends of the string that are sticking out from under the cap. Now the bottle is invisibly rigged.
--> While keeping the bottle straight upright, CAREFULLY place the bottle back in your fridge.
--> Now, if someone opens the bottle, the Mentos will no longer be held in place and will fall into the coke. Which means a faceful of coca-cola foam for them, and plenty of laughs for you.
it's great for parties, assuming you pull this on someone who can take a joke. But, be careful not to turn the bottle sideways. If you do, the coke will either shoot out from under the cap in all directions, or the cap will be blown off with about as much force as a cork being blown off a champagne bottle.
"It's easy to forget what a sin is in the middle of a battlefield." "Opposite over hypotenuse, dipshit."