Friday the 13th has inspired numerous horror movies, keeps architects from designating the 13 floor in tall buildings, and is considered an all around “unlucky” day. However, the actual stigma is of religious significance.
On October 13, 1307, King Phillip of France ordered the Grandmaster of the military/religious order the Knights Templar to be burned at the stake. This is where the stigma is thought to have originated. [By the way, all the conspiracy surrounding the Templars, as outlined in books like The Da Vinci Code, is largely without evidence]