Even with a goat, that's going to be very hard. Their bones are quite dense, to allow them to butt heads as they do.
Again, sooda, I don't care what you claim to have seen. Unless you can show some pretty strong science behind it, it's not as easy as you make it seem. It would involve forcing muscle, tendons, and then the bones themselves in a way that wouldn't so much break the neck with that motion, but tear - not sever - the spinal cord and those muscles and tendons. Not an easy thing to do, no matter how fast and hard you do it.