I found an old E-mail with the following ideas in it, and thought I'd share. I've done the one with the Tarantula, except in my case I was pet-sitting a friends snake for 4 days.....
1. Insist that you are a vegan, and protest anytime your roomie eats meat. Start leaving "slim Jim" wrappers laying around, and hold your stomach everytime they walk into the room. If they ask about the wrappers, you know nothing about them.
2. "Drink" a raw egg for breakfast every morning. Explain that you are in training. Eat a half-dozen donuts every night.
3. Every time you wake up, start yelling "Oh my God, where am I?!?" and run around the room for a couple minutes. Then go back to bed. If your roommate asks, say you don't know what he/she is talking about.
4. Keep a tarantula in a jar for a few days, then get rid of the tarantula. If your roommate asks, say, "Oh, it's around here somewhere."
5. While your roommate is out, glue your shoes to the ceiling. When they walk in, sit on the floor, hold your head and moan.
6. Wear a cape and stand in front of an open window for an hour every day. Then, one day while the roomie is out, go outside and lie under the window, pretending to be hurt, and wait for your roomie to return. The next day, stand in front of the open window again.
7. Throw darts at a blank wall. All of a sudden, start dancing around excitedly and tell your rommmate you just hit the bull's eye.
8. Practice needlepoint every night. At some point, grab your thumb and sream, "Oowwwwwwwwwwwwwww!" Cry hysterically for a few minutes, then go to bed. Sob and sniffle all night.
9.Sit in front of a chess board for hours, saying nothing, doing nothing. Then, look up and say, "I think this game goes a lot faster with two players."
10. Talk back to your "Rice Krispies." All of a sudden, act offended, throw the bowl on the floor, and kick it. Refuse to clean it up right away, explaining, "No, I want to watch them suffer."