I absolutely love reading this thread and feel it might be time for me to add my own (quite small!) celebrity stories.
When I was about 8 or 9, I went with my friend on her paper round through our village. We got to a house with a long driveway which she couldn't be bothered to walk down so asked me to do it (she was a few years older than me so of course I did what I was told). I walked down and handed the paper to a man getting out of a car who said "thank you". I thought no more of it and walked back towards my friend, only to see her stood with her mouth open before she hurriedly whispered to me "Did you recognise him?? That's Geoffrey Palmer! You know, the doctor who wants his sausages in Fawlty Towers!" Both of us and our families are big Fawlty Towers fans so I felt rather smug that I had been the one to hand him his paper as my friend couldn't be bothered (still do, in fact!)! We later found out that he had a holiday home in our village. My dad met him again a few years ago on a fishing trip and I think mentioned it to him (of course, he didn't remember, embarrassing dad!). Dad said that he was lovely to talk to. But that's probably my finest celeb story!
I have met a few TV chefs through my work as we used to have a book stall in the local Food Festival where the chefs would do a demonstration in the marquee and then do signings with us afterwards. I've met Lesley Walters (from Ready Stead Cook) a few times who has always been lovely and Rose Elliot (she writes vegetarian cookbooks) and her husband were very polite. Not so nice ones were Nick Nairn (completely ignored us, got drunk and silly by the end of the day, and stole our sharpie! Took the bottle of water we'd provided for him without even a thank you or a glance in our direction). Another year I had to stand next to James Martin who was rather indifferent to us (I just remember him being very tall and big) and was curt and rude to my colleague later on in the day who was not impressed!
We've done some other book signings over the years:
Gary Rhodes - I just remember him walking round with my boss in a big black coat looking a bit imposing. I think I remember my colleagues saying he seemed quite arrogant?
Paul Gascgoine - I didn't see him but my colleagues and some of the customers said he was in a right state; some of the customers even returned their signed books the next day as they were so disgusted

He also went into the toilet for a very long time at one point which started rumours flying!
Gervaise Phinn - he was lovely, kept making jokes to make us all laugh, very sweet.
Had an absolutely mortifying book signing session with children's author Ali Sparkes - nobody came as it hadn't been advertised properly and I had to stand with her making small talk for hours! It was absolutely one of the worst moments of my life and I try not to remember it!
Jimmy Greaves - I wish I could remember more but I'm not sure I saw him, although I was working that day (it was quite a few years ago). I think my boss, who's a big fan, had a lovely time talking to him.
We've also had a few famous faces come into our shop:
John Cleese - spoke to some of the staff and was very polite. I was on holiday in Australia at the time, absolutely gutted!! I keep hoping he'll come back.
Nadia Sawalha - being served at the till by a colleague (who said "Ooooh you're off the telly!", then had to tell me afterwards who she was). Her nan lives down our way and I've spoken to her a few times since about her famous granddaughter (she's very proud!)
Oh and once I was serving a customer who I remember being quite a big man who was laughing and made a joke which I didn't get (not unusual!). He left and then the next customer said "Do you know who that is? That was Gyles Brandreth!" I had no idea who he was so I had to google it - so I do now! But obviously I don't remember what he bought or what he said, so annoying. Now I try to make sure his books are nice and visible on our shelves in case he should pop back in!
Lastly, I'm not sure if this counts, but a couple of days ago a man rang and said "Hello, John Sergeant here" and ordered a book from me. It's not unusual for our regulars to ring and say their names as if we should remember who they are - but after the phone call I turned to my colleague and confirmed that that is the same name as the politician who was on Strictly. This doesn't mean anything in itself (we have a regular called Gordon Brown who definitely isn't
the Gordon Brown), but then I listened to an audio recording of his voice and it did sound similar! We also googled his phone number's area code and it's in one of the posher bits. So perhaps it is him, hopefully I shall find out in a few weeks when he comes to collect his book.
Phew, that was rather longer than I expected, I kept remembering more! Thanks for reading!