One friend lived with a woman who insisted on keeping everything absolutely separate, even the most mundane household items — two jars of mustard, two containers of bleach, two packages of paper towels, and so on and so forth. She would count the rolls of toilet paper on a regular basis, and a nasty altercation ensued when, once, in a bind, my friend used one of her rolls. The living situation became so tense that my friend eventually moved out, taking not only all of her belongings, but also making sure to take every single roll of toilet paper (even the half-used one in the bathroom) with her.
Another friend lived with a woman who would frequently want to have heart-to-hearts late into the night, which would often end with sobbing. This wouldn't have been so bad had it not been almost every night.
And finally, a friend of mine lived with a man who rarely emerged from his room, who slept in blue jeans, and who rarely cleaned. This man would throw garbage on the ground, even when the trashcan was nearby, and dishes would sit in the sink for months at a time. One day, the roommate called my friend into his room, which was, of course, filthy and looked like the den of a hoarder. "Does it smell like bleach in here?" he asked. "Because it smelled kind of bad in here, and I thought there might be a mold problem, so I put bleach in the air conditioner." My friend was horrified. "I thought it could circulate that way," the roommate continued. "But then I thought that might have been a bad idea." They weren't roommates for much longer.
Some of the more mundane violations I've encountered are broken objects, a failure to pay rent on time, and a general lack of boundaries. Do you have any horror stories to share?