The nestle knockout is when you fist a sexual partner in the ass while punching them in the face with the other hand. It is usually performed while having sex in the doggy style position.
The word was first used in the main stream by comedian Bill Dawes in a stand up routine.
So I put a finger in her butt, and she was like: "Umm, what are you doing?!? Put your whole fist in there! And punch me in the face! I want the whole Nestle Knockout!!!"