Gene Pitney (I just know the dead ones. lol) Wouldn't speak to anyone at the end of concert or sign any autographs. Right grumpy git so he was. .
One of the problems singers have is that they're scared of people breathing cold'n'flu germs over them, and alot of the time they're stand-offish it's because they're just trying to keep out of harm's way, especially if they're on tour and have a load more shows to get through. I'm not making excuses for rudeness but I know many singers worry about this.
As for the "don't you know who I am?" comment - the best response I ever heard to this was the receptionist putting out a message over the tannoy saying "There's a lady here who can't remember who she is. Can somebody please come and claim her as she's holding up the queue"