If a Friday should happen to fall upon the 13th of any given month then you're in trouble. We all are. Friday the 13th is considered a day of bad luck and danger in the U.S. of A. as well as most of Western Europe. Except in Italy, where they get all freaked out by Friday the 17th. Which is just crazy.
This superstition arose in part because of the unholy union of the number thirteen and Friday, which have each been considered unlucky for a really long time. So, that makes Friday the 13th like the exact opposite of peanut butter cups, which take two things that are great on their own - peanut butter and chocolate - and make one thing that is even better together.
The number 13 has been the unwelcome table guest at the all-numbers dinner party ever since Jesus's last Passover meal. Ever since that fateful meal - also known as the Last Supper by people who don't really know what Passover is - it has been considered terribly bad unlucky to have thirteen people seated at a table. The fear is that as soon as that last person pulls up a chair that one of the diners is doomed to die imminently. Another reason that mankind has been totally uncomfortable around the number 13 is that it is most decidedly not the number 12. Everyone loves the number 12. In numerology, the number 12 is considered the number of completeness. This is why there are 12 months of the year, 12 signs of the zodiac, 12 tribes of Israel and 12 Apostles of Jesus. Or, are there 12 of those things only because that number is completeness? Total mind blow. Remember, there is no spoon.
Either way, 13 is no good. Insofar as it is incomplete and may have played a larger role than Judas in the rucifiction-cay of a certain personal savior. And, this neatly brings us to Friday. Which was the day on which the aforementioned J.C. was crucified, possibly because of that whole 13-guests-at-a-table thing. Not surprisingly, Christians have viewed this day of the week a little skeptically ever since.
Of course, the holiday celebrated on the Friday during Easter weekend is called "Good" Friday. As ever, the Roman Catholic Church is ironic to the last. Those less versed in the actual lack of goodness of that day may have taken this whole good Friday thing a bit too literally and eventually opened up a chain of reasonably-priced restaurants called T.G.I. Friday's. Or they may not, but either way, there is something also ironic about naming a restaurant with an acronym that stands for "Thank God It's Friday" when, you know, Friday is very, very unlucky because that was the day that some people may, or may not (we're not here to debate the historical reality of any of this, just to deal with the anecdotal reality), have killed God's kid. So, this deity probably wouldn't be too keen on Fridays no matter how much he/she loved potato skins. Or, maybe I'm just over-thinking this.
And, from all of these mystical and religious underpinnings sprang that most spiritual of film cycles: the Friday the 13th series featuring Jason Voorhees and all manner of nubile young men and women who are doomed to be mutilated (not too long after being titillated).