Friday The 13th Superstitions: Where'd They Come From?

Today is Friday, May 13, 2011 -- the only Friday the 13th of 2011.

Friday the 13th happens at least once a year due to the modern calendar. Like last year, there's just one this year, but watch out: there are three in 2012 (January, April, July).

When you combine an historically unlucky day (Friday) with an unlucky number (13), all sorts of weirdness is bound to ensue. Hence the obsession with Friday the 13th.

Historically, some unlucky events are believed to have occurred on the day too. French King Philip IV rounded up hundreds of monks and tortured them for heresy on Friday, October 13, 1307. Some say Jesus Christ was crucified on Friday the 13th. More recently, on Friday, March 13, 1992, an earthquake in Turkey killed nearly 2,000 and left 50,000 homeless.

The No. 13 itself has driven people crazy for centuries, in large part due to Friday the 13th. Some people are so obsessed that triskaidekaphobia was born -- the fear of the number 13.

That fear has led the human race to make some strange decisions. Here are 13 examples. Vote on the most ridiculous and be extra careful today!