Differing Opinions on What Constitutes Good Television
My one roommate watched every f*cking Knicks game that was televised. We live in New York City, so EVERY FUCKING KNICKS GAME is televised. Eventually he began to only watch them in his room and that was great, until our other friend who needed to watch every Yankees game moved in. 

Pets
I've only had to deal with a pet once, and I love a dog as much as the next guy, but when your roommate brings home a newborn pup out of the blue and the thing cries through the night, tensions flare. After that fun-filled phase, the real excitement kicks in when your friend needs to leave town and suddenly the dog violently sh*tting about the house becomes your misery.

The Constant Feeling Like You Have to Include Them in Your Plans
The reverse of this problem is also a pain in the dick, like when your roommate relies solely on you as his social life and if you don't want to go out that night it means he can't go out either. But it doesn't stop when you tell them your night's boring plan. They want to go out so bad that they try to coax you into changing your mind. I can appreciate the effort, but what they never seem to realize is that trying to get you to "rally" isn't helping their cause. 

Bathroom Sharing
If you live in NYC you can bank on having to share a bathroom. And that sucks because being denied sh*t release is horrendous. Or how about waking up in the morning with a bladder full of piss only to find that your roommate, who sits on the sh*tter till his feet go numb, is having the movement of his life and it's going to be a while. No exaggeration, or pride in this confession, but I've twice had to piss out my apartment window because of that.

Having to Hear About Other People’s Jobs
You have a great story to tell, my f*cking ears want in on it. But hearing about someone else’s day or job? Forget it. Unless you’re an assassin or you managed to work a "nooner" into your day, nothing that happened in the 8 hours since I last saw you interests me.