The word GrammarNazi actually has nothing to do with actual Nazis, the word is merely something you call someone when they correct your grammar too much or rudely.
(On a group chat)
StraightOuttaTiltedTowers: Yo sup bois wanna play some fortnite?
TheRealGrammarNazi: First off, you dont say yo, you say Hey. Second off its "Whats Up", and not "sup". And finally its "boys", not "bois". Wow, so many stupid people nowadays.
StraightOuttaTiltedTowers: Bro your such a grammar nazi this aint school no one wants to be corrected.
People on the internet who dislike spelling mistakes, correcting any and everyone on their grammar in a (usually) rude manner. Nobody can escape the Grammar Nazis; they're everywhere.
Person: Your so cool!
Grammar Nazi: UM, NO. IT'S "YOU'RE" NOT "YOUR" YOU DUMBASS. YOU FUCKING IDIOT GO BURN IN HELL IF YOU DON'T KNOW THE DIFFERENCE. FUCK YOU.
Person: You're such a fucking Grammar Nazi.