Hair Removal In Shampoo
Put Nair or some other hair removal chemical in a person's shampoo or conditioner. You may need to distract the person for a moment to let the stuff take a better hold.

Lifesaver Shower
Fill the shower head with dry temper paint, onion salt, easter egg pellets or the like. Lifesavers are great since they disolve and then reform on the victim. The victim will feel sticky afterwards and of course the solution to that is to take another shower...

Sealed Shut
On a cubicle where the door reaches the floor, seal the door shut and fill the cubicle with water. You may wish to introduce marine life.

Classic Flush Toilet While Showering Prank
Flush toilets while a person showers. The more toilets the better.

Cellophane Toilet Bowl Prank
Place clear cellophane over the toilet bowl but under the seat. Works best at parties where a large percentage of the people are drunk.

Improptu Shower
Place a small tube in one or the water holes with the other end pointed outward at the victim. When flushed results in an improptu shower.

Where To Leave Toothpaste
Leave toothpast on the underside of light switches and doorknobs.

Gush Of Toilet Water
Go into the school bathroom and remove the top toilet lid. Look for a rubber thin pipe on the side, and disconnect that pipe. You will see a little hair barrette like thing connecting the rubber pipe to the plastic pipe. The next person that flushes the toilet will get a gush shooting upwards.

Out of order stall
Write "Out Of Order" on a sticker note or piece of paper and tape it to the outside of a bathroom stall. Some people will think there is something wrong with the toilet and avoid using it.

Eggs In Soap Dispenser
Crack a couple of eggs and drop them in the soap dispenser. Whoever washes their hands next will try to wash their hands with eggs.