…but never mentioned you realized they were film composers, for some reason you will never understand.
For me, that would be Marc Shaiman, with whom I once ate brunch with a bunch of other people (only a few of whom I knew) in a suite at Caesar's Palace in November of 2005. Despite sitting just a few feet from him, I never said "Hey, you're Marc Shaiman! I like your music!"
Not exactly on-topic but when I arrived at the SPFM dinner when John Williams was honored, I struck-up a conversation with a women sitting there, and at one point asked "Are you a composer?" And she answered "No, I'm actually an interviewer for E! and we're covering the event."
I reflected afterward that she was probably well-known to most TV audiences, but I rarely watched E! so I had no idea who she was.
At a friend's party many years back, I had a long conversation with David Newman about a variety of topics (opera, education, individuals rights). It was about 90 minutes into the conversation before I realized who I was talking to!
Not film composers.... but I've walked a bit with Jacky Chan once, showing him where the toilets were. (was funny - i almost stumbled of an escalator and he wanted to grab me, to stop me from falling. It was just like a movie move of his.) Didn't fall though. Phew.
Joan Chen, had a little chat with. Michelle Yeoh, a little chat with her, in an elevator - only the two of us. Jean Claude Van Damme - just a short greeting
I've had Morricone offering me cappuccino e cornetto at an hotel in Torino, while I'was interviewing him for Soundtrack! magazine back in 1991. Then lunch with Alan Silvestri in Castell'Alfero, in Piedmont, where his grandma' born. And pane e salame with Michael Giacchino in Feletto Canavese rehearsing the local band for a concert. Incredible, but true!
I had a litte chat with my half-compatriot Alexandre Desplat before a special screening in 2015 where he told me a small, hmm, let's say 'secret' about one of his very early scores - before international fame - that I won't reveal!
(But that's not what the OP was about, right? Cause I knew perfectly well - more than anyone else around! - who the man was. That's why I was there!)
I sat with some people at a Film Music Society event back in the mid 80's. It turns out at least one was a composer, but I can't recall his name right now.
(Anybody want to figure it out for me? He had recently scored a teen comedy where he got to use JW's theme from JAWS in one sequence, I think in a pool scene. I think his name was Italian-ish and long.)
Never met a composer at a hotel. However the most surprising place I did meet a composer was at the Gothenburg Book Fair (or whatever it is called in English). I did meet and had a brief conversation with Nathan Larson there because he was promoting a book he had written. On a sidenote at the same book fair I also met actor Dolph Lundgren.
I once got a delightful email reply from a 70s composer - and i was sitting in a hotel foyer at the time. Does that count?
Actually probably not because i knew who he was and he knew i knew who he was - or he wouldnt have been replying to my email. Perhaps i better start another thread - composers who replied by email when you were in a hotel foyer?