More specifically, those on StackExchange or similar Q&A sites that seem to be trolling (as in fishing) for new questions to answer solely for the potential reputation gained and/or to be viewed as a subject matter expert and to reap the rewards of the resulting stardom achieved from such activity. It seems that some view themselves as StackExchange rock stars in reading some responses and votes to remove questions that imply they are upset because the person asking the question has wasted their time and was unworthy of their attention. These types most often have the first response to a question and it is within moments of the question being asked. I'd like to get the phrase coined for this annoying behavior if it doesn't already exist.
"rep whore" is certainly closest to the mark. They're usually part of a larger tribe that I call a "kangaroo cabal," which is typically made up of half people who have absolutely nothing better to do in their lives than be "king of the heap" in stack exchange, and the second half of each tribe is fake users...sock puppets.
They exist in all the different boards. They follow each other around and upvote their own answers, and downvote all others. When it first happens to you it's annoying, until you realize that the rep point thing actually matters to them, because they have nothing else in their lives that's meaningful.
What's wrong with glory grabber?
Perhaps such a person did not get much recognition from his mother when he was a kid and would say to her, "Mommy, see what I can do," and then he'd do a cartwheel. The mother yawns and looks away. This is purely conjecture on my part, but it could happen!
We all need and crave recognition (some folks more than others, obviously). The line between a normal need and a neurotic need for it is sometimes hard to draw. Has not a single contributor to this--or any similar site--not ever bragged to someone, "Oh, I have a reputation of 80,000 on __________ site!" (shades of "Mommy, see what I can do!").