Over the course of my career, and more so now that I'm a third-party recruiter, I've had the opportunity to meet and work with a lot of really amazing people. Even a few who are famous or well-known in their sphere of work.
Thing is, if you're a Software Dev candidate (I'm including test and systems in this), sooner or later you're going to run into someone who is well-known in your world, or who you've read, or who created something amazing. And, since you're a human, there's some chance that your behavior will devolve to that of fan-boy or fan-girl. The important thing to remember is that this person across the table from you is a human, too. And though they are well-known, they still face-down the same problems you do: What do I wear today, why can't I lose that fat around my belly, I need to fire my cleaner, my car needs an oil change, jr is spending too much time in front of the Xbox this summer, etc., etc.
Pamela Slim has a great post today on fan behavior, and how to identify it in yourself. It's a great read if you're out doing interviews, just so you have a measure to check against.
Oh, and for you hiring managers out there, remember this applies to you, too. You know, when you meet Bill Gates, Steve Jobs, Guy Kawasaki, Elon Musk, Burt Rutan, Brad Silverberg, Linus Torvalds, Fred Brooks, Patrick Naughton, Bill Joy, Patrick Naughton, Marc Andreeson, David Heinemeier Hansson, etc, etc.