smc or SMC, an acronym for "Shit My Chair", is an element of internet slang created in response to ROFL, which one really can't be doing while typing. If you see something truly amazing and/or hilarious while sitting at your computer then shitting your chair is the pinnacle of reactions.
Booked a trip to London to see a girl I'm in love with and been holding out for her, spent a lot of money, and got there and she just wants to be friends! just did a SMC.
Notre Dame guy: Where do you live?
Notre Dame girl: I live in Pangborn, here at ND
ND Guy: Oh, that sucks :(
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Notre Dame guy: Where do you live?
SMC Chick: LeMans, I go to Saint Mary's!
ND Guy: Damn, that is HOT! ;)
Suck my cock. Used (mostly) by boys/men who like to piss other people off, or when they need to do something but don't want to or are too lazy to do it.