Basically everyone I know diets. Most aren't the least bit bothered by it, not enough to stop anyway. My brothers are always on some clean eating, intermittent fasting, low-carb, paleo madness. Others are sugar-free, or gluten-free, or tracking the carbs in parsley. I can't internalize any of that, or project meaning, or try to save them. I just smile and nod. Eyes on my own plate. Serenity now. LOL
If I find myself getting emotionally ruffled, I need to question which of my own thoughts are causing that. It's never the other person.
The thing that usually gets me is an "Oh, yeah! I'll show you!" competitive feeling. I was really good at restricting my food and feeling superior about it, so occasionally I'll get a flash of wanting to out-diet someone. I don't even know what kind of madness that is. Do I really want to diet again? No, but it was my thing, so I sometimes feel threatened or inferior if someone else is doing it. All it takes to snap out of it is questioning that emotion. My "why" is usually sketchy bordering on comical.