Back on topic, I don't really have any problem with eating in public. I'll admit that the dental office situation you had was certainly...novel. But I don't really see why...he shouldn't have to eat it some other time if he felt like eating it there, just because it's not convenient or not commonly done. It's the dentist's job to clean your teeth anyways. Maybe he just wanted to get the most out of his dental plan that day.
In class I'll randomly get out my lunch, set it all up on my desk and start eating it when the teacher is teaching, or we're working, even if the class is dead quiet. I mean, we're allowed anyways and if I'm hungry, so what? I'm just gonna be eating in front of them in another half hour if I don't. If someone complains about the smell or noise or whatever, I'll gladly put it away, but it's never happened before. My classmates sometimes just come up to my desk and take pieces off my lunch and eat them. I don't mind. I'm kind of like a neanderthal when it comes to food. It's not like I eat copious amounts of meat with sauce on them...for lunch I just bring fruit and bread, usually. But I do things like rip food out of people's mouths if they take it from me when I tell them not to (unless they've already chewed down more than once or twice). Or I remove their shoes and throw them down the hall, then take their lunch and run away with it, if they persist. Or I grab and twist at their chest areas.