1. Somebody who corrects another person's grammar and spelling in an ad hominem attack.
2. A label incorrectly applied to a person who corrects another person's grammar and spelling, regardless of other content in their post and the egregiousness of the errors being corrected. Ironically, this misuse of the label is itself an ad hominem attack.

(noun) one who is intent on correcting everyone's incorrect grammar

A person who uses proper English, proofreads papers for fun, and gernerally corrects everyone's improper grammar. This person feels very ashamed when he or she is caught making such errors and corrects himself/herself often. It should be noted that a Grammar Nazi simply wants to help others and does not correct others out of arrogance.

where you go into youtube comments, and you find people correcting people.

A person who has mastered the art of speaking the English language. They are best known for going on social media and constantly correcting the incorrect usage of other users, and are almost universally hated by everyone. An occasional correction does not signify a Grammar Nazi, that title is earned after months of corrections.

KEEP IN MIND: Many people who are corrected by a Grammar Nazi really need the public shame because they've put too many poorly-written statuses on their social media accounts, and the Grammar Nazi should be hailed as a hero. If the person in question is clearly not a native English speaker, then the Grammar Nazi is the villain

Grammar Nazi's are by far the most hated people on the internet. Due to the simple fact you know in daily life their ether absolute nobody or somebody with nobody.

So they feel they have to adjust spelling and grammar because they genuinely believe that spelling, and grammar is the only way to live.

I would love to say grammar Nazi's are similar to Trolls (see Trolls), However this is not the case. They actually do get angry at unreasonable grammar, Even though they seem to forget that planet earth is multicultural and English is not some peoples first second or third language. However Grammar Nazi's only usually speak one language English.

Grammar Nazi's can only be found on the internet This is due to their absolute coward ness outside the world wide web. If a grammar Nazi was to exist outside the internet there head would presumably explode this is because in the real world, most humans speak somewhat slang, and if a random grammar Nazi was to correct someone on the high street for example, they would get the hardest punch on the face they could possibly receive.

I am the human version of a pokedex and this was about the human type Grammar Nazi

A person on the Internet that uses proper spelling and grammar. They usually dwell on forums or other social websites and correct the grammar/spelling of, or insult those who have improper grammar or spelling.

The Grammar Nazi will be hated by the person targeted by "He who spells". The "victim" will usually resort to useless insults.

It is a sophisticated form of trolling. The end result is serving the duty of the Grammar Nazi, and causing the idiot to be enraged.