One who insists on dictating what others should call themselves based upon their diets. The food nazi usually is very insecure and desperately strives to belong to an "elite" group of people (usually vegeterian or vegan), causing he/she to try and exclude as many people from that group as he/she can, by resorting to lowly and immature insults.
Food nazis should be approached with care, as their unstable and volatile state of mind could cause them to burst out into violence if they are of the suspicion that the other person is better than them, which is true for 99.99% of the population.
Joe: "FUCK YOU ASSHOLE!!!! If you eat fish you're a pescatarian! I'm a vegan, I'm amazing and morally superior to everyone everywhere! I am of equal rankins to God because I don't eat anything animal! You're a stupid pescatarian!!! FUCK YOU!!!"
Bob: "yo chill dude.....stop being such a fucking food nazi! You sound just like that Aaron MacGregor on Facebook...what a douchebag!"
Me: Genetically-modified foods and aspartame and MSG and trans fats are your Reichstag Fires, you Rockefeller-funded Food Nazis! You're just like the Rothschild-funded Nazis!
Food Nazi: Pay no attention to the deranged conspiracy theorist! We do not receive Rockefeller funding! We never advocated trans fats! Anybody who says so is a shill for the food companies!
Me: HELLO?! MARCH 1988 NUTRITION ACTION NEWSLETTER ARTICLE TITLED "THE TRUTH ABOUT TRANS: HYDROGENATED OILS AREN'T GUILTY AS CHARGED"?!
Food Nazi: Don't make us sic our SS stormtroopers, I mean the police, on you and tase you!
You: better watch your ass the Food Nazi is right there.
FOOD NAZI: ohhh little boy you better eat your sandwich before you eat your ice cream!
Person 2: Oh yes, I know who you're talking about. someday, "Hitler" is gonna get a gun on her head, robbed and killed and the store is gonna catch on fire with a flamethrower.