I've performed with a handful of celebrities. It turns out Tim Russ is a really good blues/rock guitarist. Just a couple of weeks ago, I shared the stage with Beck at Davies in San Francisco, as part of his Song Reader project. And got hit by a door driven by his eye-candy assistant (accident -- it was real crowded in the wings). There were a bunch of other celebrities in the wings, though I didn't perform with any of them. I even provided entertainment for a Buzz Aldrin speaking event once.
Every last one of these guys was 100% gracious. Beck gave a ton of free autographs (though I didn't ask for one -- I really don't have the heart to pester someone like that).
I have no sympathy whatsoever for someone who isn't.
The two celebrities I've performed with were Yo Yo Ma and Luciano Pavarotti. Since I was just one of many musicians in the orchestras, I didn't have occasion to interact with either of them on an individual basis, but I was mightily impressed by their musicianship. I'm not an autograph hunter, but I still have my parking sticker, with Pavarotti's picture on it, stuck to the outside of my bassoon case twenty years later. I'll never be able to replace that case - I'll just have to keep repairing it when something breaks!