Today's Austin American-Statesman (click to see illustration by Don Tate) informs me that fear of Friday the 13th is called "paraskevidekatriaphobia."
I've blogged about F, the 13th before, but I will note that according to the Statesman article, the number 13 is considered unlucky because of there having been thirteen guests at Jesus' Last Supper (the last of them supposedly being Judas). And as for Friday, that's when Jesus was actually crucified. However, Italians consider the 13th lucky. Interesting, eh?