A repwhore (correct English: reputation whore) is a whore who likes the reputation of a online forum and thus asks everybody to give him or her "rep" (short for reputation).
When asking *cough* begging *cough* for reputation, most of the time you will get a derep (correct English: negative reputation) unless you are cool and/or a oldfag or maybe any other reason.
Noobs might beg for reputation the whole time, but it's best for you and me to ignore this person or (if possible) give him or her a negative reputation (a.k.a.: derep) because that is what they hate most.
In good situations these noobs might even kill themselves which will make the world a little better.
Noob: oMg gib m3 repz0rs~!
Oldfag/Cool person: Give me rep or you won't get account, because I am a repwhore.