I've never understood the Friday 13th thing;
Friday 13th is purely manmade and only applies to one calendar which has been meddled with quite a few times over the years.
If you believe that SOMTHING is in control of Life, the Universe and everything and it wanted to create a 'bad' day, then it would make it related it to somthing in its calendar, like full moon Solstice or whatever, not to somthing created by mere mortals.
Wouldn't it?
Mike