I used to be superstitious as all hell. Seriously, a bad hand of cards would seem like an omen to me. Fortunately, I’ve (mostly) outgrown that. So Cracked’s look at dumb superstitions is a great read. Here’s there explanation of why cats are bad luck:
It didn’t help that a number of pre-Christian peoples such as the Norse, Celts and Egyptians had cat gods, or at least considered the animal sacred. Once Christianity became the sexy new religion in town, old beliefs were branded witchcraft and cats found themselves guilty by association. Often simply owning a cat was considered proof of witchery. There was even widespread extermination of cats during medieval times, which kind of backfired when they were no longer around to kill plague-infested rats, which in turn wiped out half of Europe. Whoops. But hey, at least they were safe from those goddamn witches.
We had nothing but black cats when I was growing up. Of course, maybe they were the reason I couldn’t get lucky in high school.