Today is the lone "Friday the 13th" of 2010.

Friday the 13th happens at least once a year due to the modern calendar. There's only one this year and one next year (May 13, 2011), but watch out: 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 very unlucky events were said to have occurred on the day. French King Philip IV rounded up hundreds of monks and tortured them for admitting to 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 long driven people crazy, 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 and exhibit unusual behavior in the past. Here are 13 examples. Vote on the most ridiculous and be extra careful today!