A 'skullfucker' is someone who fucks you in the skull. Either in the eye socket, or mouth, or anywhere else where the penis can penetrate the skull, such as a hole smashed in the back of the skull with a hammer so you can feel the brains on your cock and shoot semen directly onto the area that gives people horrifying nightmares of dicks entering their skulls and shooting semen into their brains to impregnate them with the children of the master race of skullfuckers.
Suzy's a slut, she'll give you skull for weed.
Ashley skulled me all night till I busted in her throat.
Malicious mockery, directed at one individual, with the intention of causing that individual mental and emotional anguish on a comparable level to having their eye socket violated with a hard cylindrical object.
1: That was some pretty serious Skullfuckery there man.
John realized when he turned the lights on that the fantastic blowjob he had been receiving was no blowjob at all; instead, the woman had removed her glass eye and he was engaging in skullfuckery.