Probably the easiest way to tell him that you're not interested in being anything but roommates and friends is to say "Hey, I don't want us to be anything but roommates and friends."

But seriously, just don't get into the "mixed signals" department. Make sure you're body language isn't sending a different message than you're intending him to receive. If you have a tendency to be flirty or touchy-feely with guys, make a conscious effort NOT to do so with this guy. Have guys over, talk about your boyfriends, and treat him like one of your girlfriends -- unless you have a tendency to makeout with your girlfriends.

But remember, horny/desperate/interested guys will interpret anything you say or anything you do to mean "maybe she's interested in me". Try to stay away from comments like "wow, I wish I could find a guy like you" or "wow, you look really good tonight". You don't want this guy mistakenly thinking he makes you hotter than your the stash of naked Brad Pitt photos you keep under your bed.
[Editors' Note: As soon as "naked Brad Pitt photos" was mentioned, one of our female writers immediately began getting fidgety in her chair, excused herself from the room, and came back seven minutes later looking extremely disheveled and flushed in the face. We're not really sure what that was all about, but as soon as she returned, she asked for a cigarette and had a certain glow about her.]

Anyway, moving on from the masturbatory habits of our female staffers.... if all else fails and you really want to make sure he doesn't think of you as more than a friend, try you might want to try some combination of the following drastic measures:

• Let him see you shaving your armpits.
• Wear shorts around the house when you haven't shaved your legs in a really long time.
• If you're in the room when he's watching baseball, yell "touchdown!" when you see a homerun.
• If he's watching football, say "Oooh, that meanie looked like he was trying to hurt that nice boy running with the ball."
• Occasionally "forget" to flush the toilet after taking a huge shit.
• If you're ever hanging out alone with him, make sure you have Mexican food with lots of beans for dinner and feel free to fart away. The louder and smellier, the better.
• Keep all your sexy underwear hidden in your drawers, but occasionally leave a pair of big 'ol granny panties lying around [extra points if they've got shit stains].

If all that still doesn't work, well, then we can't help you and it looks like you've got yourself a genuinely obsessed, creepy, psycho-stalker, wannabe-boyfriend living with you. Good luck!

-- The College Guy

P.S. If you really try all the above measures and this guy STILL wants you, then you must be DAMN hot and you should ditch the obsessed roommate and move into the extra bedroom at AskTheCollegeGuy.com headquarters.