Roommates are fun to pick on

I find my self often doing things to mess with my roommate. Nothing malicious or mean, just make him question who it is he's living with. For example...

-When ever I have a free moment when he's not here, I will change the TV channel to something odd that he nor I would watch. (think spanish music channel)

-Throw odd stuff in the toilet bowl (peanuts, bloody tissues twisted like a tampon)

-Change the operating system on the computer once a month

-Take out the trash---wait, I'm suppose to to that :P

If anyone else has some good ideas, I'm open for suggestions!