Paraskavedekatriaphobia

or, fear of Friday the 13th.

According to this article I read a few years ago, 9% of Americans think Friday the 13th is jinxed. I guess that not's that bad, statistically speaking. In that same article, this oxymoronic gem appears, "Religious authorities have often warned against putting faith in superstition."

Hmmmm.

It seems from what I've read online this fear of Friday the 13th didn't crop up until the 19th century, and it's an extension of the fear of the number thirteen, or "triskaidekaphobia." The Friday and the 13 were brought together in a novel from 1907, appropriately entitled Friday, the Thirteenth, by Thomas William Lawson. If you're feeling really adventurous, you can read the book through Google book search.