Well, there's the cockiness, but there's also the fact that many times those words are code for "slave". My first job was like that. They advertised for "rockstar" .Net programmers. Only, in this case, "rockstar" apparently meant "willing to work 18 hour days for no extra pay or benefits save the manager telling you how awesome you are and how much money you're saving the company". Ever since that, I've looked at job postings looking for "rockstars" or "ninjas" with a jaundiced eye.