Now you're probably wondering why you would want your roommate to hate you and the answer is simple: I have no idea, but it makes for a pretty sweet article. It's pretty easy to annoy another person. It's even easier to annoy someone who lives five feet away from you.
1) Strike up a conversation. Start off with, "So I was whacking it in the community bathroom. You know, the one you shower in every morning?" This is sure to piss him off a little. He'll give you a look of disgust and maybe say something to the effect of "you're a douche bag," that's when you know you've really struck a chord.
2) Speaking of chords, playing an instrument is a surefire way to anger your roomy. A guitar isn't too annoying, unless you suck at it, which I coincidentally do. Fortunately, practice makes perfect and no one practices more and at the most inconvenient times than me. Studying for a test? I'm practicing. Talking to your girlfriend on the phone? I'm practicing. Trying to sleep at 4 in the morning? I'm sitting in your computer chair whacking it" then I'm practicing. And by all means, feel free to play an obnoxious instrument. I recommend a tuba, a full drum set, or a xylophone.
3) I don't know if I've mentioned it yet, but whacking it is a pretty standard way to annoy your roommate. Everyone tries to hide it in college, but we all know you do it. What you're going to do is beat it when you know he'll catch you. When he leaves to take a piss, pull out the Jergins and the porn and go at it. When he returns he'll be thoroughly disgusted. See that look on his face" it's priceless.
4) Comment on family pictures. "Is that your sister? Wow, she's got a great rack for a twelve year old." If that doesn't make him mad comment on his grandma "Do you think I have a chance with your nanny" because your grandpa just died last week it's cool, right?"
5) Stare at him. When's he's on his computer, stare at him. When he's watching TV, stare at him, when he's sleeping, stare at him. When he's staring at you, act like you got something in your eye, then when he turns away, stare at him. He'll feel pretty uncomfortable and not want to spend much time in the room. Congratulations, you have more time to practice the guitar (jerk off).