Flour Under The Door
Pour some Flour on a thin piece of carboard. Unfolding a cereal box would work great! Then slip it under a door and blow it all over the inside of the room. If you know the person is going to be gone for a few days, try blowing powdered sugar as it will attract ants.

Shaving Cream Door Bomb
Fill a manila envelope with shaving cream, then place the open end of the envelope underneath your victim's door and stomp on it as hard as you can. It will explode all over the inside of the room.

Classic Cup Of Water On Door Prank
Leave the door open about 5 inches or so. Enough to place a cup of water on the top of the door. When your victim opens the door, he or she will get a waterfall on their head.

Cereal Falling
Take a paper plate and tape a short string underneath it and tape the other end of the string to the fridge door. Make sure to place the plate of cereal on top of the fridge. When your victim goes to open the fridge door, he or she will get a plate of cereal falling on their head.

Escaped Prisoner
Dress yourself in an orange jumpsuit and sneakers. Shave your head and put a handcuff on one wrist. Then go knocking on people's doors asking if you can use their phone. Works best if you try this prank in a neighborhood where a jail is nearby.

Waiting For A Friend
Hold the elevator door open for a long time and tell everyone inside that you are waiting for a friend. If they get pissed after a few minutes, tell them your friend specifically told you to wait and not go up yet.

Elevator Door Jam
Tape a small piece of cardboard near the top of the elevator entrance door so it doesn't close.

Elevator Jam
Take a large group of friends with you into an elevator. Go up and down for about 15 min. Nobody will be able to go inside even though their floor door will open, because the elevator will already be jammed with riders.

Refrigerator Door Graffiti
Place some clear scotch tape on the fridge door. Be sure there are no creases. You don't want the tape to be detectable. Then write on the clear tape with red nail polish. When your victim sees his or her fridge with writing all over it, they will freak. When they do, just pull the clear tape right off.

Hey! You cannot go in there!!
This prank would work best in a building with many doctor or professional services offices. Simply place a sign on their door that reads "Authorized Personnel Only" It helps to print the sign in big red letters.