Its odd, meeting famous people sometimes. It doesn't happen very often to me, but even outside the office you can bump into them, in Soho, on their way to or from somewhere. They're generally fine about people being appreciative of their work.
I saw Guillermo del Toro a few years ago, but didn't even get a chance to embarrass myself by saying anything as he was talking to other people and clearly in the middle of something. Then I saw him a couple of weeks later, on a tube train, with his family, on a day out somewhere.
That time I decided not to be a fanboy and let him have his day off without being bugged.
Even after one of his kids stood on my foot.