I'm in graduate school so I've been in college for a long time, and most of that time I've had roommates and most of them have been weird. Coincidence? Definitely not.
The fact of the matter is everyone is weird up close. This means that in casual, infrequent interaction most people can come off looking pretty normal, but when you start living with someone, that’s when stuff gets weird.
This is because the real person will only come out once you’ve spent enough time together. Nobody can stay on their best behavior 24 hours a day, seven days a week. Eventually the uncensored version is going to come creeping out, and when it does, be ready. It’s like Animal Planet, you’re observing human animals in their natural habitat.
Living with someone puts you at ground zero when it comes to bad hygiene. Some roomates don't shower. Some roommates I’ve had shower but don’t use soap. Others don’t shower so that they can put the time they saved by not showering into playing World of Warcraft. One guy never showered, he just washed his hair every few days in the bathroom sink with antibacterial soap.
Another thing that will differ wildly is personal boundaries. For instance, when I moved into one place my roommates and I sat down and agreed to share our stuff. I was thinking that meant eating somebody’s Pop Tarts if you were out, or possibly watch their Transformers DVD.
Then I was walking home from school one day and saw one of my roommates driving my car, whereupon I proceeded to lose my mind. Turns out he thought sharing cars was part of the sharing deal so he had helped himself to my keys and run a few errands all over town. I get to borrow his shaving cream, he gets to borrow my car. Totally logical.
Another roommate I had would just open my door and walk into my room without knocking or anything, which is unbelievably alarming. I was like, “Dude, you can’t just walk in here! I could be naked! Or I could have a girl in here! Or both!”
That’s not likely, but still. It’s the principle of the thing.
And dude also did not know how to say "excuse me." He would just push past.
But nothing lets your peer into a person's sheer lack of initiative like living with them. Most of my roommates have never had jobs and spend their days watching TV, DVDs, TV on DVD, playing video games and occasionally going to class. Honestly, I'm way jealous.
And I never would have discovered these things about these guys if I hadn’t lived with them. That’s why couples divorce and separate, because once they start living together they start to realize they married a weirdo.