I think my worst roommate story is pretty impressive: When I was fifteen, for a few months I rented a room from a twenty-one-year-old college student. It was purely a business arrangement--I answered an ad in the paper--and I was a good tenant: paid my rent, cleaned up after myself, didn't invite people over. He, however, decided I was evil, and, one night while I was sleeping, slashed the cushions of his couch and performed other quiet acts of destruction and then called the cops on me, claiming I was the culprit--and a trespasser, to boot. I was awakened from a sound sleep by a knock on my bedroom door, followed by interrogation. Apparently, I came off as more credible than my wacko roommate, because nothing came of the matter. I do remember being so astonished at what he'd done that I was laughing about it, and perhaps my light-heartedness persuaded the police of my innocence. My roommate got what he wanted even without my arrest, though, for needless to say I didn't stay there much longer.
I'm pretty sure the guy was going through some kind of breakdown, because when I saw him a few months later he had shorn his hair and taken to calling himself Allison (his named was Allan).