Paraskevidekatriaphobia*

Culled from a lot of sources but mostly Wikipedia 

It's weird the things that bother people, superstitions abound particularly in this country over Friday the 13th. It dates back to the French/Papish extermination of the Knights Templar back on Friday 13th October 13, 1307, though there is some suggestion that it was on Friday the 13th of October 1066, that the decision was made by King Harold II to go to battle on Saturday the 14th of October, rather than allow his troops a day of rest (despite his army having made a long and arduous march from a battle near York just 3 weeks earlier), thus making it a bad day to make decisions. 

Even crossing the road can have consequences, though only if you're female and Scandinavian, Finnish researchers in 2004 claimed that men are no more likely to die in traffic accidents on Friday the 13th than on other Friday, but Finnish women have a two-thirds greater chance of getting killed in a Friday the 13th crash. Mind you, if you're Dutch it appears to be safer as the Dutch Centre for Insurance Statistics (CVS) on June 12, 2008, stated that "fewer accidents and reports of fire and theft occur when the 13th of the month falls on a Friday than on other Fridays, because people are preventatively more careful or just stay home.

Still, thanks to the vagaries of the Gregorian calendar the 13th of the month is more likely to fall on a Friday than any other day of the week.

In fact, in any 400-year period, there are 685 Monday the 13ths, 685 Tuesdays, 687 Wednesdays, 684 Thursdays, 688 Fridays, 684 Saturdays and 687 Sundays. 

(Each Gregorian 400-year cycle contains 146,097 days (365 × 400 = 146,000 normal days plus 97 leap days), 146,097 / 7 = 20,871 weeks, and 400 × 12 = 4,800 months. Thus, each cycle contains the same pattern of days of the week (and thus the same pattern of Fridays the 13th), but no day of the month up to the 28th can occur the same number of times on each day of the week (because 4,800 is not divisible by 7). The 13th day of the month is slightly more likely to be a Friday than any other day of the week.On average, there is a Friday the 13th once every 212.35 (212 and 241/688) days.)

 Personally I believe you make your own luck, however if the day is of significance to you, be careful out there.

*Paraskevidekatriaphobia, fear of Friday the 13th