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1.
GfaC started back in the 1920's, due to the reign of gangster Al Capone, who had a habit of stabbing you in the face and shooting you in the back and giving you new concrete shoes and finding new uses for woodchippers. Because of this, getting killed by his gang became known as being "Caponed", later shortened to "'GfaC" for no known reason. GfaC's current form comes from a typo in the name.
A fatal GfaC that you will remember for the rest of your life, and also may turn you emo. GfaCs are like getting ur face sat on by an elephant or decapitating ur testicles by accident.
by [GfaC] Sigma June 11, 2008
 
2.
GFaC means Go Fuck a Cow. It is widely considered a step above the common insult 'Mother-fucker', due to the fact GFaC involves fucking a cow.
Roger: You are so annoying Melissa, why don't you just fuck yousfelf?
Melissa: Why don't you just GFaC?
Roger: Shit, I've been owned.
by Gendrik Fillimore Adam Cormal August 01, 2013
 
3.
GFAC means go fuck a cow.
Chandler: Brittany knows things
Alex: Brittany can GFAC
by Abizzle768768768 August 04, 2009
 
4.
Go Fuck A Cow!!

enough said...
Your so retarded, gfac
by MRS MaiNeRS September 17, 2006