Turn around the batteries of the tv remote and watch as your victim tries to surf different channels.
Post signs on a park bench that say,"caution: dry paint". sit down next to the sign. laugh at people who come and try to tell you not to sit there!
Superglue some coins to the sidewalk or any spot that has a lot of people walking around. make sure it's an appropriate place, then watch people break fingernails to get the coins.
Cat and mouse: cut a tiny piece of paper to fit undetected under your target's computer mouse. write `gotcha!` on it then stick it on the device with some tape. when they try to use it, it won't work. a peek at the bottom of their mouse will let them know they've been pranked!
Take an empty suitcase. pick it up and carry it like it is really heavy. go to the victim and ask them to carry it somewhere for you. they'll be unprepared for such a "light" load.
Post signs on a park bench that say,"caution: dry paint". sit down next to the sign. laugh at people who come and try to tell you not to sit there!
For teenagers: get a realistic-looking fake tattoo. put it on some part of your body that can be partially seen, then accidentally expose it to your parents & enjoy the reaction.
Get a balloon and put it on the tailpipe of a car and make sure the car isn't already on. then get in it and have your parents start it up and it will pop. it will sound like the tire popped.
Salt and pepper: open up a salt shaker and tuck a piece of paper towel over the top, then fill it with salt/pepper and screw the lid back on. the person using it is in for a surprise!
Pour some yellow food colour into the cistern(tank) of your victim's toilet. then wait for your victim to use the toilet. the victim would try to flush the urine but won't be able to flush it down!
Take a needle and thread and run it through every pair of underwear/bra in the victim's drawer, so that they are attached in one long string. when they get dressed, they will grab one pair but end up with so many of them.