Regarding the pp's encounter with Ruby Wax, I "met" her in a theatre bar just before lockdown, having just seen a play by David Baddiel (who was also there and is THE LOVELIEST MAN ON THE PLANET). My friend was rather tipsy and said loudly "ooh, look, it's Ruby Wax!" (I hadn't noticed, she was standing in a dark corner with some friends) and immediately went over to tell her how much she loved her. I half-expected RW to be a bit dismissive but after 10 minutes she still hadn't come back so my other friend and I went over to find her deep in conversation with her about her daughter, who was in a play in the studio theatre in the same building. She was absolutely delightful and very gracious towards the drunkish woman invading her Saturday night.
Similarly, I was once in a (amateur) play in a theatre at King's Cross in the 90s, we were having an aftershow drink when one of the cast suddenly looked up and ran out of the pub. He returned dragging Su Pollard with him... she was dressed to the nines in something feathery and glittery on her way to a nightclub, but didn't seem to mind one bit that this guy had dragged her into a dodgy boozer to meet his friends (nor did she seem offended that his introductory line had been "Su Pollard!!! My mum loves you!"). Anyway, she was also lovely.
Rudest famous person I've ever met was Suzanne Tully from Eastenders. Again the early 90s, I'd volunteered to man a phone for Children in Need, the centre was in Docklands and the organisers kept bringing the (locally-themed) celebs round to say hello to us, vast majority were lovely (especially Kenny Lynch, even though I didn't have a clue who he was) but she had a face like a slapped arse the whole time, wouldn't do autographs or speak to anyone, just stood there with a gob on her.
I've also been completely ignored by Ian McKellen in a conversation because his attention was completely on my male companion. Which was nice.