An emphatic, incredulous rejoinder to a statement, which indicates one's utter rejection of that statement as being so far beyond ridiculous and/or stupid that no further discussion of it is merited, warranted or tolerable.
Like, OMFG...you hate the Bieber?? FFS!!
Dude, are you seriously going to use Justin Bieber in your Urban Dictionary Definition example?? FFS!!
2.) An infamous acronym on the GameFAQs.com message boards meaning "Fox for sex." The meaning of the phrase is unknown.
2.) excuse me, everyone! Fox for sex. That is all.
"FFS, to your left."