a) To "gently" persuade someone that your opinion matters more than theirs. Which of course it does.
b) A way to end a futile attempt to lift the awareness of the obviously ill-informed person with whom you're interacting (e.g., an asshat, buttmunch, fucktard, or similar).
* Usually used online during intellectual discourse, but rare instances have been discovered in letters involving spats between romantic partners (see white trash).
aaron: STFU! my gf's hot, and all y'alls moms are ugly, skanky hoes. FUIUD!!
fred: yer mom ain't winnin any prizes either, dude
don: hang on - yo, take that out of your mouth and look up at me. I'll have to disagree - except for the lazy eye, aaron's mom is bangin' ...
aaron: fuck off