That's an irrational fear of Friday the 13th (the date, not the films -- which were enough to send anyone screaming from the theaters, not because they were frightening but because they were frighteningly bad, but that's another story).
According to an item in USA Today, this phobia affects approximately 21 million people in the USA (although the source for this statistic isn't sharing his/her data).
Personally, I'd not have known it was "Friday the 13th" until someone or something (such as an article in USA Today) pointed it out. In my mind, today is not a bad luck day. It's the 13th of the month.
And, as it turns out, the 13th of July is also the wedding anniversary of one of my sisters and her husband, and to them I wish all happiness and good health.