I am a vegetarian and now gluten-free. Within my restrictions, I am an adventurous eater. Vegetarian is easy. Adding the gluten free makes it much harder. I am now the most boring person in the world to eat with unless I am cooking. But I haul around protein supplements and as long as there is something I can eat, and I am not expected to eat all meals at places where all I can eat is a tiny side salad, I keep my mouth shut. I think that is polite -- as long as there is something on the menu for everyone, that should be enough. However, there are great vegetarian restaurants and cuisines all over the world, and it would be nice if we could go to one of those restaurants at least once. I mean, since I am eating side salads at Chez Meat the rest of the time and chugging protein shakes in my room. Courtesy goes both ways, IMO. In OP's position, I would have called the discussion very quickly and said, "I am going to Chez Fried Rice. Join me if you like. Otherwise, I will see you at Place, at Time." Nothing impolite about that.