Friday The 13th
One of the most popular superstitions of today is Friday the 13th. This day is commonly associated with bad luck and people tend avoid business meetings, weddings, and other large events. Due to the fear of so many there is actually a phobia for the day, Friggatriskaidekaphobia.
It is largely known that Fridays and the number 13 are unlucky by themselves. Much of this superstition goes back to early Christianity. Friday's have been quite unlucky in the christian faith. Apparently, Eve bit the forsaken apple on a Friday. It is said that this was also the day of the great flood. As for the number 13, Christianity also shows that Judas was the 13th member at the last supper and Jesus Christ was crucified on the 13th. Many other religions take note that the number 12 is especially lucky where 13 is unlucky.
Superstition grew fast in the middle ages during the rein of King Philip IV of France. The day the King would torture the Knights Templars would be Friday the 13th. Many movies have been created based off of the fear of the day as well.