1) Someone who is too stupid to think of a reasoned response to any argument so resorts to attacking someone's grammar and spelling instead.
2) Someone who has failed to grasp that forums are not in fact English essays. Language has always varied according to context, just as we use different types of words in a job interview compared to with our mates.
3) Usually in English forums monolingual native English speakers who utterly FAIL do to the fact that 60% of times they are criticizing someone who is using English as a second language at a far higher standard than the grammar nazi would ever be able to use a second language themselves. 30% of remaining cases the person they are talking to is native English but is dyslexic or 10 years younger. And all 100% of times the person being criticized has much better things to do with their time than correct their every spelling mistake. In either case the grammar nazi fails!
4) Someone unable to figure out the difference between intelligence and correct grammar and spelling.
1) erm.. I don't understand. Brain hurt. Damn why do I have to be so stupid? Oh well- let's just insult his grammar and I'll feel intelligent again.
2)Grammar Nazi"You didn't cite your references or write a proper conclusion- you can get an F for that essay"
Normal Person"erm... Lol it's not an essay its a forum post!!!"
Grammar Nazi"eh? I'm confused? Where am I? Who am I?"
3)Grammar Nazi "You use 'their' not 'there' DUMBASS!"
Janic : Sorry my English isn't up to your standards. My native language is Czech so maybe we should switch to using Czech. As you suggest you are more intelligent than me due to my lack of English logically you must be able to speak fluent Czech as well."
Grammar Nazi "oh... erm... errr" FAIL
4)Grammar Nazi "Your arguments are invalid as you lack the intelligence to use apostrophes correctly"
Philosopher: "Hmmm... Intelligence... what really IS intelligence? In our culture we have learnt to.... (intelligent discussion of intelligence)
(Grammar Nazi's head explodes at this point)