A reputation nerd is a preson whose post count on a forum speaks about his lack of social life. He is very famous on that particular forum, altough 95% of his posts usually have no substance. He is not a troll, but can choose to be, and others will still tolerate it. His messages are the filler junk you have to scroll through to get to the useful posts about a subject. He replies to every subject on the forum, even if he doesn't know anything about it, just for the sake of commenting.
On occasion, other reputation nerds with not so much thousands of posts will agree with the dominant alpha-nerd just to get his approval, and that is the difference between him and a troll. But the reputation nerd doesn't care, or rarely shows any emotion at all. If he does show emotion, it is usually fake and exaggurated.
In this case, Kid A is the reputation nerd
Kid B (10 posts): I'm looking for this game (explains game)
Kid A (10 thousand posts): It's torchlight rofl
Kid B: Oh, thanks man
Kid A: no I was joking, it is not torchlight. I don't know what it is.