Paraskavedekatriaphobia.

I just found out that's what a fear of Friday the 13th is called.



From Wikipedia:
History of Friday the 13th

Before the 20th century, although there is evidence that the number 13 was considered unlucky, and Friday was considered unlucky, there was no link between them. The first documented mention of a "Friday the 13th" is generally listed as occurring in the early 1900s.

The Last Supper, with stories that Judas was the thirteenth guest, and that the Crucifixion of Jesus occurred Friday.

That the biblical Eve offered the fruit to Adam on a Friday, and that the slaying of Abel happened on a Friday (though the Bible does not identify the days of the week when these events occurred).

That it started on Friday, October 13, 1307, the date that many Knights Templar were simultaneously arrested in France, by agents of King Philip IV.

More Friday the 13th info here and here