Someone once tried to teach me the 'shoulder snap' but I don't think I could ever get it right.
Apparently there was only one guy in that whole gym who could and while he was a hard hitter he was also one of the larger guys there and not the only hard hitter.

I'm not sure if it was a real technique or not now especially since someone is teaching the hip snap. Could there really be two types of snap used in boxing with some only having heard of the shoulder snap and others the hip snap?