OK folks, this from the horse’s mouth on one of his CD collections:
He worked at a piano bar for 6 months after signing a bad contract. He figured he was going to give these guys any of his work, and hopefully he could get out of the contract. “Piano Man” was written about that particular gig. [And therefore it must have happened before the song’s release, which IIRC was 1973]
The old man was real, though obviously some creative license was taken with the “making love to his tonic and gin” line. And the real guy didn’t rhyme when he asked him to play a song. [Joel was unclear whether or not he said the “younger man clothes” line specifically…]
John was the bartender, and he did get free drinks, though the job sucked otherwise. [No mention about the movie star line.]
Davy was in the Navy…
The waitress was actually his first wife, who was a cocktail waitress.
Businessmen did get stoned…
People did ask him what he was doing there, saying they knew somebody in the business or that they could produce for him…
And finally, Paul was a real estate broker who would get drunk and would go on about how he was writing the “Great American Novel”.