Has anyone dealt with a narcissistic partner?

@SkeetSkeet there was one when his two kids and my son were all in the car. I was on the phone with Amazon and asked everyone to be quiet so I can talk. Of course being that they are all 8 and 9 they couldn’t help but to make noises. But suddenly my new husband turns around to the back and smacks my son on his knee. My son got startled and started crying. The husband says it wasn’t that hard and ignored the situation. I thought that was a very strange reaction. Why hit? And why only my son in-front of his children when they were all doing the same thing.