Why and when did Friday the 13th become an unlucky day?

There's lots of different origins here's links to a couple

http://urbanlegends.about.com/library/weekly/aa101100b.htm

http://www.urbanlegends.com/misc/friday_the_13th_origins.html

http://www.globalpsychics.com/lp/Superstition/friday_13th.htm

This is an interesting site also:

http://home.att.net/~OneWorldWeekly/13.htm

The early suggested origins stem from the fact Christ began his journey of crucification on a Friday (Jewish Sabbath) and the number of original Apostles + Christ, made 13 members at the Last Supper.

That is one suggested reason.

All this info has been interesting. Personally I love Friday's the 13th....it's kinda my special day. Don't ask me why. Guess I'm just "special"

That day is only unlucky for those who deny their good fortune, by default, in their focus on bad luck.

So while all that extra good luck is in the air, I reach up and take it, as if it were a shining brass ring waiting to be seized..