#5: Smaug from 'The Hobbit'
Obviously, Smaug would be a hoarder. Your dorm room would be constantly cluttered with useless stuff, but since none of it’s technically yours you can’t exactly throw any of it away in the trash (which of course neither of you wants to take out because you’re both convinced it’s the other person’s turn, so what you have going on is a Jenga tower of garbage slowly piling up).
You would try to clean up a bit and he would snap at you for touching his things. As a result, you would live in absolute filth and resent him for it.