1. Buy a cheap car window pane, break it into several pieces and put it on the drivers seat. Ideally, place the pane on the seat and then break it. Ninety percent work is done, now you just have to roll down the window pane, on the driver side of the car, sit back and enjoy. When your friend returns, he will be dumbfounded to see that his car window has been shattered.
2. Here's a simple prank that is always good for some cheap laughs. Place an object on the floor where you know someone will bend over to pick it up. This object could be a book, an important looking envelope, a purse, etc. Position yourself nearby with some scraps of cloth that tear easily with a noisy rip. You can also use a strip of velcro to create the tearing sound. The prank is simple. Just wait until the mark bends over to pick up the object. As with many pranks, the timing is critical. At the precise moment that the mark bends over, rip the cloth. You'll be surprised at how many people reach around immediately checking for rips.
3. A friend of mine pulled off this trick which he said he learned in Penn and Teller's book, "How To Play With Your Food". At a Chinese restaurant with a group of people he opened his fortune cookie and threw the message down in disgust, saying "I knew I shouldn't have eaten here". When another guest picked up the fortune it read: "The Chef spit in your food". My friend had eaten at this restaurant before and copied the format of the fortune cookie message and duplicated it on his computer with custom messages.
4. This is a trick you can pull with the sprayers that are on sinks on pull-out hoses. Put a rubber band or piece of tape around the lever so that it's locked the "on" position. Aim it towards where you're standing, to where you want it to hit the victim. The next person to turn the water on will get sprayed.
5. Here's an obnoxious little prank known as "the sneeze". It's always good for a cheap laugh and it's harmless. Cup some water in your hand. Now sneak up behind your victim and sneeze loudly. At the same instant splash water on the victim's neck. They will be disgusted to think that you slobbered all over them in such an uncouth manner.
6. Get 40 or 50 paper cups filled with about 3/4 of the way up with water and arrange them on the victim's desk, table or floor. Arrange all the cups into a big cluster. Now staple them all together near the top of the cup. Now the victim is faced with the dilemma of how to remove all these filled cups without spilling water all over the place.