A year or two after we left uni, my friend turned up at an event with her 'new' partner. We were all in our very early twenties and this bloke was then maybe in his 40s. I kept loudly asking "What is X doing with that old bloke?" Apparently, he was Jimmy Page from Led Zepellin, who all my friends recognised (and idolised, and couldn't quite believe he was spending the evening with us) but I had no interest in that kind of music, and didn't know him from Adam. He sat at our camp fire and sang and played an acoustic guitar, and they were all so star struck to have sung with him. But I kept being objectionable because I had no idea who he was. He was actually lovely.
I also once spent all evening (a Thursday, early 1980s ) out with someone who was No 1 in the charts and on Top Of The Pops that very evening (well, his band's video was, as he was with us). And I didn't realise til afterwards and someone told me, who we'd been singing with all night (as this was a Folk Club and his band was decidedly pop).
Once at a party I chatted most of the night with a bloke who had one of the main roles in 'The Bill'. I had no idea who he was. But he looked vaguely familiar. So I chatted with him, hoping it would come back to me whether he was the bloke from the market, or the man from Tescos, or... (My ex was an actor in a cockney TV thing). It was only afterwards ex told me who he was, I realised I kept seeing him in trailers for his show - which I never watched. Apparently he enjoyed talking to me because I wasn't star struck.
I also once stood on Feargal Sharkey's foot. I was wearing heavy army boots at the time. It was the height of his fame and he was probably playing the city where we lived but not looking where I was going, I walked right into him, on the street and stood on his toe. His roadies or whatever they were, looked ready to swing for me.