My FiL eats with his mouth open and refuses to close it, even when asked.

I do hate being asked a question as soon as someone sees I have put something in my mouth! So rude, I feel obliged to speak with my hand over my mouth to answer.

As for DS - yes, I do tell him to close his mouth as he eats. We need to neither hear nor see food in the process of being eaten. BUT... when he has a cold, I tell him to take smaller bites and worry less. I had a perpetual runny nose as a child (food intolerance) and eating with my mouth shut was SO hard. I did my best but my dad just ridiculed me if I had to open my mouth to breathe, no matter what I said to explain it. I'm not going to be that draconian!

We also don't put elbows on the table.