You should've gone up to him and been all like "I think you're MagNEAT-O!" Have you seen that episode of Extras with him in it? That one's amongst my favorites. (
http://youtube.com/watch?v=IbHupZTS_iY)
Good gawd people! This is SIR Ian McKellen! HE'S WITH THE ROYAL SHAKESPEARE COMPANY FOR THE LOVE OF GAWD!
That's it, you are all...barbarians!
...besides, I prefer him as Gandalf. And I heard he's pretty strict in real life.
Oh, and I almost caught him and the stage crew coming out of the Esplanade in a van. Damn tinted windows though...