From SuspireWiki

noun (pl. -s)

1. A person who uses proper grammar at all times, esp. online in emails, chatrooms, instant messages and webboard posts; a proponent of grammatical correctness. Often one who spells correctly as well.
   1. A person who believes proper grammar (and spelling) should be used by everyone whenever possible.
   2. One who attempts to persuade or force others to use proper grammar and spelling.
   3. One who uses proper grammar and spelling to subtly mock or deride those who do not; an exhibitor of grammatical superiority.
   4. One who advocates linguistic clarity; an opponent of 1337-speak.
   5. One who corrects others' grammar; the spelling police.
2. proper noun
   A nickname, pseudonym or handle for a well-known grammar nazi (defs. 1 and 2) within a particular social circle, used to show either great respect or great contempt for his or her abilities.
3. verb (transitive)
   To correct the grammar of (a person's speech, a piece of writing, etc.); to edit for grammar and spelling; to proofread.

Examples:

• A grammar nazi knows the difference between "there," "their" and "they're."
• Teh grammar nazis haev invadd r formu.
• Grammar Nazi, help me with my English homework please.
• He totally grammar nazied my article, replacing pronouns and rewriting clauses.