Now, its been a while since I've lived in the dorms, but my memories of RA's are still vivid. Basically RA's are the biggest losers on campus, they're usually 22 year old nerds that don't drink or party and jack off to cartoon porn. Here are some ways to make their lives miserable.
Fuck his girlfriend
-She is probably ugly and/or fat, but it will be worth it once he comes into his room to see you on top of his woman and all her rolls.
Put weed in his room
-RA's hate drugs and call the cops whenever they smell incense. Get a bag of some shitty weed, hide it in his room and then make an anonymous phone call to the cops... they will take care of the rest.
Duct Tape his door shut.
-In the middle of the night get some duct tape and completely cover his door with it so he can't get out. Do this every couple days. He'll be late for his classes and fail out of school.
Fart in his room
Simple and easy, every time you have to fart, just walk on in, say hello, and let 'er rip. Eating pounds of cabbage and cheese will make it more fun.
Order shit on his phone
Ask to borrow his phone, and grab his credit card. Then buy some medication from a commercial, some "urban" ring tones and the Ab-fex 3000. He will be delightfully surprised until he gets his credit card bill.
Replace all his liquids with mustard
-This one takes some time, but its well worth it. Get a huge jug of mustard and replace all his shit with it. Instead of fruity shampoo he has a head full of mustard. Instead of brushing his teeth with minty toothpaste, he gets a mouth full of mustard. And instead of jacking off with KY, he'll have a dick covered in mustard.
Spill your drink on his computer
This will be an accident. Just come into his room bullshitting about the last episode of Heroes or something and then... oops! my drink fell on your computer. This will break his computer and all his cartoon porn will be gone.
Punch him in the fucking face.
-And run away
Hopefully these tips will help ruin your RA's day and/or week, and will kill time in between classes. Good luck my friends.