Go to the junk yard, find a the same model of car that they have, preferably one in very poor condition and swap out the interiors.
Imagine getting in your car and realizing the seats are a different color, and smelly, as well as several other parts of the interior of the car.
It takes about 30 seconds to remove the backseat of a Honda accord, just 2 bolts. About 15 seconds to remove a front seat, about 10 seconds to remove the paneling around the radio.... You might need some practice for speed, but it doesn't cause damage, if you get caught the cop will believe that its just a prank cause you have duplicate parts. Watching somebody get in their house/car and then wondering if their in the wrong house/car is priceless. Getting spare parts will be a bit of a hassle, as well as learning how to quickly dismantle the car, but actually doing the prank will be quicker than you think.
Or you could just spray deer musk on everything.
Or poor raw eggs down the crack between the window and the door. Smells soo bad and is impossible to get out w/o dismantling the door.
Deflate the tires.
Go to a butcher shop, get all the spare guts he will give you, apply to car.
Put doggy doo doo underneath the handles/steering wheel. When he grabs it ewwwwww.......
Fill condoms with a little bit of mayonase, put in back seat. Drop a flier for hookers/"escorts" somewhere where his mom will find it.
Buy an HIV(or other STD) home testing kit, leave instruction booklet and "a how to live with a STD" booklet somewhere where girlfriend/mom will find it.
Put a voice activated recorder under his seat, see what you can find out. Leave audio cuts of your findings around the school.
Get to the fuse box in the car...... replace all fuses with blown ones. Leave good fuses in trunk/glovebox.
Get under the hood and disconnect the alternator or drain the battery.
Remove all the tires of car, leave on cinderblocks. I've seen this done in 30 seconds flat with 4 guys! Thats 1 minute for 2.
I'm bored u do some thinking now.