So, it's interesting that society likes to pretend that people don't want attention, or don't deserve attention unless it falls within a very narrow (and increasingly getting narrower) band of "socially approved activities", but at what point do we just all throw up our hands and acknowledge it's bullshit?
I mean, so what if cosplayers are "attention whores"? You know who else is? Actors of both stage and screen, comedians, magicians, singers, people who perform in bands, jugglers, anyone who rides a unicycle in public, dudes with outrageous hipster sideburns, that annoying guy at the ren fair that's pretending to be the town cryer, etc, etc, etc.
Sure, we don't expect people (currently) to go "Oh man, that Beyonce Knowles is such an attention whore with all her singing and dancing" or "Did you see that touchdown that Tom Brady threw - what a damn attention whore!" but that's only because we seem to have this arbitrary point where you earn enough money that your "attention whoring" ceases to be for self gratification (as if) and turns into a respectable career.
The whole thing is really quite ludicrous when you think about it in any amount of detail. You could be the most annoying person in the world running around screaming "LOOK AT ME! LOOK AT ME!" 24/7 (think: reality tv star) and so long as you can pretend to make money doing it, then people will justify it as acceptable. That ought to tell you just how pathetic the criticism is in the first place!
"Attention whore" is simply an insult thrown at anyone who gets more attention than the insult-er thinks they deserve, which is not up to them, really.
There are people who suffer from extreme narcissism, but that's a whole different bag o' monkeys.