When used on messageboards, notably Collegehumor's, it means that some douche has gotten a first by commenting before the picture/article/video has gone national
(Sample thread)
Kokopelli 3 days ago:
F1RST!!
P.S. I'm a douche
Gary from California State 1 day ago:
I second that.
ean 1 day ago:
yea you're kind of a douche for future posting