I saw Colin Baker in the street when I was about 5 and shouted Dr. Who at him, he stopped and chatted with me and my mum.
I saw Princess Margaret at my primary school for some reason when I was very young.
I was in a play with Sylvester McCoy before he was famous.
My mum knew Richard O'Brien so met him a couple of times.
Saw Keira Knightley in a cafe in Teddington, many moons ago.
I once caught a plane from Brazil to Germany in 2006, with the whole Brazilian football team on board.
Another football related one was getting into a lift in Peter Jones with David Luiz and his mum (and auntie and sister I think/assume).
Most recent one was seeing the queen going through the middle of Brixton (never figured that one out) and quite a sight, 70 odd police cars followed by HRH in her Rolls (they were going at a lick too).