Gripping the snake behind the head can actually injure it if done incorrectly. Many/most conscientious snake wranglers these days only use snake hooks unless they absolutely have to hold it behind the head, such as for instances where you need to milk the snake for venom. There is absolutely no reason to do it to your pet, and as Reinz said, you're destroying the snake's trust by handling it roughly/unpleasantly.

I do touch my snakes on the head gently, to desensitize them to it, and help build their trust that hands by/on their heads means nothing bad will happen. I do this in case I ever need to hold their head for any reason, such as administering medication or removing a foreign object that might have gotten trapped in their mouth. Strudel is to the point where she will allow me to make a lose fist around her head and is still chill as a fall morning about all of it. You don't want your snake to be fighting you as soon as you get it out of the enclosure, so work to build a relationship with the animal and treat it with respect.