There's nothing more satisfying than a well planned and executed practical joke on your buddies. Just the sheer simplicity of a practical joke and the pending mayhem is so rewarding. But please keep in mind some people handle a good practical joke better than others, so attempt these at your own risk.
Ride Damage Survey
This practical joke is best done to people who are truly anal about their car, truck, whatever. The type that parks their car a half a mile away from the mall to avoid it getting touched by human kind. When your buddy leaves the car, get your friend to place a note on the windshield that reads "Sorry, about the scratch. We will take car of any damage." and add a fake phone number. Then as you come out with your buddy from the mall, and they read the note, let the search for the non-existent scratch begin. You can help by point out "potential" scratches, watching him or her run over to see, only to realize it's just dirt.
I Didn't Type That!
Microsoft Word and most likely a bunch of other word processing programs now come with something called "AutoCorrect". News flash: your cell phone does too! When a common misspelling is made, it checks a list for it, and makes the corresponding correction. Example, it would change "adn" to "and". The magic of this is that it is user editable! Hop onto your co-workers workstation, load up their word processor's AutoCorrect list, and let your imagination run rampant. First start with the small, but most aggravating ones by reversing what is already in the list, change the corrections to the misspellings! Then move to even more humorous stuff like company acronyms, people's names, it's endless! Then watch to see how long it takes before they switch the blame from their own typing, to the word processor, and eventually to their sick minded co-worker... you! Everyone knows you can do this on your friends' phones but it's funnier to do it on your coworkers computers!
Superglue a quarter to the ground in front of a vending machine. Watch how cheap people really are.
In countries that use speed cameras, park your car on the side of the road at night, preferably somewhere you can hide well. As cars pass you, take pictures with your camera, the flash will lead the drivers to believe they have just been caught speeding. Watch the glow of red lights as they slow down after realizing they just got a ticket for speeding. Too bad you can't be there to witness the months of anxiety waiting for the non-existent traffic violation to arrive by mail to all these "speeding" drivers.
Teacher or professor giving you a hard time? Grab their blackboard chalk and drill a small hole straight down from the writing end, insert a match, and fill the hole with a blend of chalk dust and glue. Put the chalk back and watch the panic when smokes starts to spew! Warning: you may go to jail for this.
Show Your Colors
Place a "Gay Pride" sticker on your homophobic buddy's car. The joke only gets more amusing the longer the person doesn't realize it is there. This works great for people that reverse into parking spots and tend not to walk around the back of their car.