Can moving the.neck to quickly or popping the neck kill you or break your.neck or sprain it?

On necking....: Gently moving the neck and then popping it like you might your knuckles may be OK if you are careful and just do it once in a while, but it can become a habit and then do more harm than good (in addition to making you look like an out-take from "The Exorcist"). Yes, people can cause a sprain and even a partial dislocation if not careful. A competent chiropractor can do it effectively if he's good.

Not likely: You would have to have a significant defect in the cervical bones for them to break by moving your neck on your own. Popping your neck is unlikely to break it or kill you. You may be forceful enough to sprain it.