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.
Used in full when spoken, or as the acronym 'FFS' in texting/chat environments.
Tweener: There's never been a singer like Justin before...like, never, ever, EVER!
Non-Tweener: Woah, FULL FUCKING STOP!!
Justin Bieber is your idol?? FFS!!
Like, OMFG...you hate the Bieber?? FFS!!
Dude, you really plan to use Justin Bieber in your Urban Dictionary Definition example?? FFS!!