Mostly the titles mean aboslutely nothing and more or less correspond to the amount of posts you've made.
Now there are some 'custom' titles out there and whenever I update the software, it resets everyone's title which is an enormous, nay GARGANTUAN pain in the arse because there are so many users.
The "Vegas Rock Star" thing is because it's paying special 'homage' (doesn't pronouncing "O-mazh" just sound cool?) to the people that made it out to meet up in Las Vegas.
But largely, beyond that, the titles are arbitrary and I really wish the software engineers that develop the software would do away with them entirely.
You should have seen the fracas when we had user ratings.... Lordy lordy lordy, "Doug, I had four stars yesterday, but now I've got three, is someone mad at me" (yadda...yadda...yadda...)