The act of fucking someone's skull, especially through the eye socket.
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.
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.
2: Yeah, she's crying in the corner like you just raped her puppy.