Met Tom Selleck when I was about 8 yrs old, summer of Jedi(83). I was on holiday in London with my family when we walked into what we thought was a large indoor market. Turned out it was a movie set of a market and we walked into the middle of a shoot with Tom Selleck about to tear through on a motorbike. They were cool about our mistake and Tom came over and talked to me for a minute or two, he gave me his autograph, was very nice. I knew who he was but had never watched an episode of Magnum in my life, still haven't.
Seen Alex Cox, director of 'Repo Man' and 'Sid and Nancy', again in London(different time though), in Oxford st when I had just came out of Forbidden Planet. I was a kid at the time and recognised him from presenting BBC2's 'Moviedrome'. I must've gave him some kind of unintentional bug eyed stare because that's exactly what he gave me back in return.
John Densmore drummer of the Doors at a book signing. I made an embaressment of myself at that one, tried to be funny but was just weird.
Dave Prowse as Darth Vader at a signing. Round about teh time Jedi came out, after he was given the boot by Lucas for sharing secrets of the Jedi(return of) with the press he did a lot of signings, totally crushed your hand when shaking it.