Before I tell my roomie stories, I'd hope that everyone remembers that we only see things from our own perspective, perhaps some of us, maybe most in fact annoyed our roommates as much as they did us. Just a thought.
Last year was my first year in college and when I moved in, I had know real idea about who my roomie was other than his name, major and where he was from. Unlike seemingly everyone else on the floor, we really didn't try to contact each other before move in. Luckily he was a really nice guy.
I think with regard to him, I was the problematic one, although he has his own quirks as well. He almost certainly had OCD (I have OCD too, but not with regard to the same things as him). Every weekend he'd go home since he lived about 30 min. away, and every Friday before he left, he'd clean and straighten everything up which was great, just not to the extreme detail that he did. Mind you, I never actually saw him clean anything, or do anything that would account for how perfect everything on his side of the room was, but he had to have done it. Nevertheless, I cam back one day and he had gone so far as to line up and categorize the magnets on our refrigerator
Otherwise he was a great roommate, for that matter, his extreme cleanliness doesn't make him a bad one. The problem for me was that he went to bed at 10 or 11 every-night and I'm a night-owl, so I avoided our room after that point till I went to bed at 3 or so which created problems whenever I wanted to do homework in the room and needed an internet connection since we don't have WiFi in our dorms.
Also, I'm by no means a dirty person, but I can be a little messy. The problem for me was that, once I started dating this girl, I spent most of my time over at her dorm (she lived in a single) so my crap would pile up on my side of the room since I was never there. So whenever I'd come back, stuff would be overflowing from around my desk and bed, I'm sure that didn't make him all too happy.
I also liked to leave our door open so people could just wander by and pop in, I'm not really the keep to myself type person that he was. In retrospect, this probably wasn't the nicest thing I could have done whenever he studied or anything.
After my first semester, I moved down the hall with one of my buddies. I actually moved out of a room with a roommate that was extremely clean and went home most of the time (I'm an idiot apparently).
My buddy and I imagined that this was going to be great, we were pretty close and he stayed up late at night like me plus he was really social so having people in and out of the room wasn't a big deal, especially since they were usually friends of both of us.
Problems soon became evident though . . . .
Him and I were about the same size, so he'd borrow my clothes (he'd ask first, and I didn't really care, but it was a little weird).
He would blast his music, which if he had taste in music, I wouldn't be too upset about, but I can only take so much Gwen Stefani before I want to shove pencils in my ears and hope to damage my timpanum.
He was also extremely hyper and demanding, which made me glad that he started going home all the time.
He drank far more than I did, and this became more apparent toward the end of the year when he would go out ever night of the week and then go home on the weekend. His extreme drinking would cause two instances which I are going to stay with me for quite some time.
One night, he came back and got into his bed and started making coughing sounds, so I looked over the edge of my bed to check on him and he mumbled to me and stopped coughing so I didn't think anymore about it. The next morning the sheets were off his bed and he had gone home for the weekend. I didn't find out until I started to smell something in my room that he had thrown up in his bed that night. And the only reason that I found out was because one of our friends knew. That wasn't the bigger problem though, it was that he had left the vomited on sheets in his hamper in the room over the weekend.
And the worst thing that I experienced was, after the vomit sheet incident, he had come home from drinking one night and I was already in bed. He got into his bed (ours are bunked, remember that) and I fell asleep. Around 3 AM, I wake up and see him get out of his bed and stand up beside it, he pulled down his boxers and starts peeing on the floor at the foot of his bed. I had to stop and question if I was actually seeing this, and yes, yes I was. I can only imagine how much he had to drink because he seemed to go on for about 2 min. All this time I was yelling at him to get him to stop and he didn't even respond to me. He eventually got done and got back into bed. I was in shock, but I was tired and had a test in the morning so I did the only thing that I could do, I climbed down from my bed and jumped across the spot that he relieved himself and grabbed the febreeze and soaked what I thought was the spot and went back to bed. When we got up the next morning, I asked him if he remembered what had happened last time, he told me no, and I said "You pissed on the floor!" He looks at me like he had just figured out some riddle and says, "So that's why my clothes are soaking wet."

Not only had he taken a leak on the floor, it had been the same spot where he had all his clean clothes piled up, so they got soaked in the process.
For the rest of the year, if our room ever got hot, you could still get a whiff of urine.
What's even worse is the fact that my brother experienced his roommate doing something very similar to this when he was in college, only instead of the floor, his roommate would pee in his own bed and get back into it.