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1.
Acronym for 'Go suck a fuck', as immortalized by Donnie Darko's sister.

Quoting:
Donnie: You are such a fuckass.

Elizabeth: Did you just call me a fuckass? You can go suck a fuck.

Donnie: Oh, please, tell me Elizabeth, how exactly does one suck a fuck?
"You are totally messing this one up, aren't you? "GSAF already"
by Okki March 07, 2012
 
2.
Abbreviation for 'go suck a fuck'. When used, it refers to the ever so endearing 'fuck off' or 'fuck you'. The line appears in the twisted movie Donnie Darko, released in 2001.
Donnie: You are such a fuckass.
Elizabeth: Did you just call me a fuckass? You can go suck a fuck.
Donnie: Oh, please, tell me Elizabeth, how exactly does one suck a fuck?

Maddy_Just_Fucked_U_Up: so i hear ur a whore :d
xterrorsexscenex: dude, gsaf
by rachaeleatsrazors February 17, 2010