A Friday occurring on the 13th day of any month is considered to be a day of bad luck in English and other countries in the world. This superstition began in the early 1900s. Although there is little documentation as to why this is a bad luck day, there are stories that people have spread throughout the world to maintain this "bad luck" status.
The story of the Last Supper, with stories that Judas was the thirteenth guest, and that the Crucifixion of Jesus occurred Friday. The story where 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 specify the days of the week when these events occurred). Another popular story is that it started on Friday, October 13, 1307, the date that many Knights were arrested in France, by agents of King Philip IV.
For those of you who are extremely superstitious, make sure you try not to freak others out. I hope nothing bad happens to you. The next Friday The 13th will be in July so take note and prepare yourself--haha--Take care!