I’m talking specifically about the martial arts style neck-twisting move. Is there anything stopping a person from grabbing their head and doing a quick twist manuever to break their own neck (aside from a reason why or the nerve to do so)? Is there any sort of defense mechanism that would stop you from doing it?
On a side note, is it really as easy to snap someone’s neck as its portrayed in movies? Do any schools of martial arts actually teach the move?
Speaking from experience, most definitely yes. Now excuse me while I dial 911. 
I came damn close to doing this in high school. Chin in hand, boring lecture, up all of the night before, . . . I fell asleep and my head fell forward with no resistance. I didn’t break my neck but the snaps, crackles, & pops would have put a chiropractor to shame.
A few years ago I read in a newspaper that some guy broke his neck and died. He used to twist his head causing popping noises claiming it made his neck feel better. One fateful day he gave his head a twist, went to far and severed his spinal cord.
I don’t know about the “movie style” twist but yes, some martial arts do teach neck breaking. I happen to have a video…:eek: