Skullfucking has only ONE literal meaning, which is to fuck a person's eyesocket.
It does NOT refer to fucking them in the mouth, throat, ear, makeshift hole, or anywhere else.
"You know skullfucking means to fuck your eyesocket, right?"
"It does? Nevermind then."
2. See mindfuck.
3. Can also be used as a kind of insult.
2. Damn, watching Memento will give you a bloody good skullfucking.