Please excuse me posting in this old threat, but minor celebrity sightings...
Pretty much the entire WWE roster of 2003/4, I was mad into wrestling when I was little and stayed at the same hotel as the wrestlers, got tonnes of photos, Chris Benoit put me in a headlock in the pic, quite eerie looking back at it now.
Paul Chuckle (of Chuckle Brothers fame) in Blackpool about 10 years ago, my friend's Dad shouted "no slacking!!" at him, which went right over my head.
Richard Ayoade (The IT Crowd) whilst walking through a tube station, stared intently at him for a few moments trying to work out who he was then it clicked when I was about 300 yards past him.
Bill Drummond (The KLF) came to my school to speak to the students doing Drama A-Levels, I didn't know about it so didn't really meet him, would like to have asked about Extreme Noise Terror collaboration.
Various members of semi-well-known Japanese pop groups (namely BiS) around the streets of Tokyo, this is a very loose use of the term celebrity i'll admit.