And how the heck do you say "paraskevidekatriaphobia"?
I just learned what is means. See this excerpt:

"Paraskevidekatriaphobics — people afflicted with a morbid, irrational fear of Friday the 13th — are no doubt pricking up their ears just now, buoyed by evidence that their terror may not be so irrational after all. But it's unwise to take solace in a single scientific study (the only one of its kind, so far as I know), especially one so peculiar. I suspect it has more to teach us about human psychology than it does about any particular date on the calendar.

The Most Widespread Superstition

The sixth day of the week and the number 13 both have foreboding reputations said to date from ancient times. Their inevitable conjunction from one to three times a year portends more misfortune than some credulous minds can bear. Folklorists say it's probably the most widespread superstition in the United States: some people won't go to work on Friday the 13th; some won't eat in restaurants; many wouldn't think of setting a wedding on the date.

How many Americans at the turn of the millennium still suffer from this condition? According to Dr. Donald Dossey, a psychotherapist specializing in the treatment of phobias and coiner of the term "paraskevidekatriaphobia," the figure may be as high as 21 million. If he's right, eight percent of Americans are still in the grips of a very old superstition.

Exactly how old is difficult to say, because determining the origins of superstitions is an imprecise science, at best. In fact, it's mostly guesswork."

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Urban Legends: #13 for more.