People who tell you what to eat

I'm a vegetarian. People cringe when I tell them that. I swear they brace for attack, like I may jump all over them about health and animal cruelty (both totally important things). I'm not that kind of person. However, judging from the reactions I get, people are quite used to being preached to by my vegetarian and vegan friends.

And it goes both ways. Once, while out with friends for pizza, I simply said I would order something separate since they were sharing a pepperoni pizza. One man at the table, who I hardly even knew, was all over it like white on rice. He asked "You a vegetarian?" I responded affirmatively. "Why? Why do you even do that? You aren't making a difference. You aren't even more healthy than me. They have studies about how bad for you a vegetarian diet is." Jesus Christ dude.

Why do people do stuff like this? Food is so personal. It's akin to trying to tell someone who only wears bikini briefs that they are stupid for not sticking to thongs or a fair mix of both. It shouldn't matter to anyone else but you what underwear you wear or what your diet is (unless you are obese, in which case I'm sure your Dr. and family members are worried too). Live and let live. If you can't do that, you are probably a douche bag.