Thank you for asking this question. It sounds like the culture of his family — meaning his family’s value system and manner of interacting with each other, over influences him when he’s back home. Do not tolerate this. Next time it happens interrupt him and say something about it so that he understands what is happening in the moment. I appreciate how difficult this is, and that it will be uncomfortable to do — but your job is to set the boundary about what is acceptable and what isn’t. It is not something he’ll be able to fully understand after-the-fact. You’ve tried this, and it doesn’t work. Tell him when he is doing it that you don’t like it, that it is rude, and that you don’t like how you feel when he does it. This is important for your future together. You need to have a voice and talk about what’s wrong the moment it happens.