A person who is n00bish because in reality they are mentally retarded. They don't act stupid to annoy people, they ARE stupid and probably don't mean to piss people off. In all honesty, it's impossible to tell who's a n00b and who's a r00b unless you know them in real life.
I thought Rob was a n00b who liked bugging people until I met him. Turns out he's really a r00b.