A nutsock is a sock in which you repeatedlymasturbate into, until it is all crusty and rock like and continue to throw it at the bitch that has driven you to crust up the sock to that degree, knocking her out.
Girl: "Eww why the hell is this sock rock hard and crusty"
Guy:" It's a nutsock, I need it cause you're afat ass bitch and that sock lets me nut inside it"