I can't say I've had anything as bad as the stuff people have listed on here, but I have had roommates that just simply bugged me. (I think I mentioned this guy once in another thread.) Near the end of the semester, I was checking the thermostat on an almost daily basis to make sure a certain someone hadn't set it to 55 degrees. 55 degrees. During winter semester.
The guy also could cook. Which wasn't a bad thing, except when he'd leave it in the pan overnight or something. I'll come into the kitchen in the morning and his pan of dried, crusty stroganoff is still sitting in the pan on the stove.
And, no offense to anyone here, but I don't like tuna at all. This guy did, and whether he knew it or not, he made it clear to the rest of us. He wouldn't rinse out a can of whatever he'd open, so I had the "privilege" of coming to the kitchen, with the smell of old tuna hitting my nose like a brick wall.
And I found it rather disturbing that this guy would frequently blast some awful rap, or even Britney Spears or Shakira or Destiny's Child.
Jam it back in, in the dark.