My mom brings me food in my room the most of the days. When she does, I interrupt whatever I was doing and I stare at her for the whole time she is in here.
Sometimes she forgets or generally when I'm really hungry I go to the kitchen and I grab random junk food, however if she sees me doing this then she starts coming at me (but she doesn't know I see her) and I retreat into my room before contact is made.
Other times she says "dinner is ready" and that means that she won't bring me food and I should go to the kitchen to eat, unless I explicitly ask her for it.
When we had guests she always brought me meal unless that was people from my family and I'm forced to eat with people and the stupid TV background noise.
I can manage this for a short time and it depends on the person if I consider it polite or not to stay at table or to immediately retreat in my room.
Once I didn't feel very well because it was a long dinner with people who are supposed to be near me. I zoned out while at the table, I put my sweatshirt hood up and my state must have really been noticeable. I was questioned aggressively about it and I didn't feel like answering so I got away and I went to bed, everyone else came in my room and started yelling and they left, I don't remember much but I felt very sad and angry.