Just in case you like to pull pranks on people, i got bored and thought i would give you guys some ideas.
1) Take some oreos. Pick one oreo and take out the icing. In its place, use soap or toothpaste! Give oreo to unuspecting victim. When person asks what is in the oreo, gladly reply by saying you have no idea. Just in case this person goes to the bathroom to clean it out of thier mouth, put some tape on the faucet so the water sprays all over them.
2) Get a roll of clear cling-wrap. (this one takes a while if you want it to turn out well) Put cling-wrap on toilet seat. Make sure that you can't see it, or else the prank will be ruined. And don't be an idiot and mess it up by using the toilet before the prank is pulled off. If you do, then you are a major dumb ass. Anyways, i think you know what happens when someone uses the toilet later. Some other fun ones that have a similar idea are to put toothpaste, glue, and honey on a toilet seat.
3) It is kind of mean, but you can slip some chocolate laxitives into someone's candy.
4) Put raisins into someone's toothpaste to look like bugs.
5) Put some money on the ground. When someone comes by and bends down to pick up the money, you rip a piece of cloth. This makes them think they ripped thier pants. I know its corny!
6) Put black shoe polish or nail polish on someones phone (make sure you can't see it. if you need to you can change to color to match the phone) and then you call them (dont be an idiot and wait for it to dry. call them while it is still wet).
7) Take a bar of soap. Put clear varnish or nail polish over the bar of soap (yes you can have the color match the soap). Wait for when someone goes to take a shower and the bar of soap won't lather up. To make it better, take out all other soaps from bathroom and shower so they have no other soap.
8) This one works well for people in offices. You take the keys on a keyboard and switch them around. Be careful not to destroy the keyboard. If the person can type without looking down, they will be really confused. If they are one of those "search and destroy" typers who always look down before pressing a key, then they will still be confused.
9) This one also works well for people who work at a desk all day. You simply move all contents of each drawer. So when they look for a folder, they can't find it. Yes, this could have bad results so don't get too crazy.
10) Remove a bathroom doorknob. Then you put it on backwards. So the lock is on the outside. Then you lock the door and leave it open. When someone goes in and closes the door, they will not be able to get out and will wonder if they locked themselves inside. And little do they know, the lock is on the outside and they are stuck in there until you let them out.
The next few are for the bathroom
11) Glue shampoo bottles closed.
12) Glue shampoo bottles to counter so you can't pick them up.
13) Scrape off the top of someone's deoderant. To make it look normal again, put some cream cheese!
14) Put food coloring in someone's soap. Then when they go to wash their hands, it gets worse as they use more and more soap.
15) You have to wait for the right moment with this one. If someone is at your house and they really have to pee, you get to the bathroom first. (make sure they don't kow if you have another bathroom) Have a huge bucket of water hidden under the sink. You slowly pour the water from the bucket. The other person will start to think that you really have to pee and they will really really have to pee. Just make sure they don't pee on your stuff. Because that is just nasty.
16) This one only works for women. You go into the restroom at a movie theater, mall, some public place. When you go in, take a bottle of sprite, mountain dew, or a similar soda. When you are in the stall, you shake the bottle and let it spray everywhere. Be sure to get some into the stall next to you where someone else is. As this happens, use the excuse of "Sorry! I have bad aim. I'm kind of new at this.". Yes, if there is a line of people, prepare to be humiliated! But in the end, it is totally worth it. Because yes, i have tried it and it worked very well.
17) Put a hair removal cream, such as Nair, into someone's shampoo.
18) The classic prank of flushing every toilet in the house while someone showers.
19) Crack some eggs and drop them into a soap dispenser.
20) Pour vingegar into someone's mouthwash.
21) Take the lid off the cistern of a toilet. This is where the part that control the flushing is located. Then pour in some bubble bath liquid and some pink food coloring. The next person to flush the toilet will get pink bubbles everywhere!
22) When you see that your friend's shampoo bottle is running low, fill it back up with hair dye! Of a totally different color than the one their hair currently is!
23) Put food coloring into someone's tootbrush. When they use it next, their teeth will be a rainbow of color! If you want the color to last longer, add some salt.
24) Place dry ice in urinals and toilets.
25) Put real or fake poo (clay and baby ruth bars work too) in a urinal!
26) Put black duct or electric tape on automatic sensors in bathrooms. Then the toilets won't flush and the sinks won't work. Don't put any on the soap dispensers. Then they will have soapy hands and no way of cleaning them!
27) Stir dozens of boxes of Jello mix in a toilet. Let it sit overnight and the next morning there will be Jello in the toilet!
28) Put shaving cream in someone's toothpaste.
29) Fill your friend's bathroom sink with water, continue to dye it yellow. Then clog the reserve drain.
30) For this one, you must work quickly and quietly. When someone uses a porta potty, unscrew all of the walls. If this works correctly, the walls will drop.