Calling someone a slut; Implying that their pussy is loose after having sex with them...
Basically calling someone a sock full of lube and it being like a slut's pussy- since its loose. Insulting someone with a poor sense of humor.
"Dude, have you had sex with Kayla yet?"
"Yea, man...Shes such a
Sockfuck!"
"Dude,take a joke and lighten up...You act like a
sockfuck..."