I read somewhere a long time ago that Friday the 13th was an arbitrary date picked to execute prisoners in the Middle Ages. Not sure if that's true, but I guess that would make some sense that a date would get a bad rep.
Now, not all bad things happen on this date. My Mom won a contest on the 13th, I won the elementary school candy sales for the most sold one year & my daughter was born on the 13th.
I look at it, along with black cats, as good luck. Just me.