Stands for "suck my rather large cock".
Can be used in a wide range of circumstances ranging from having just won an internet battle/debate, losing an internet battle and being proven wrong, or just as a simple insult.
User1: Dude, no. youre wrong. vader NEVER says "luke i AM your father."
User2: what are you TALKING about?! yes he does. its one of the most classic scenes in movie history!
User1: youre an idiot. he says "no, I am your father"
User1: *link to youtube
with scene in question* SMRLC
User1: Sonic would beat the shit outta mario.
User2: dude....mario is waaay more popular than sonic, so stfu
User1: We're not talking about popularity! were talking about who would ACTUALLY win in a fight!