Who is the disco king? I had always thought that Nile Rodgers was the disco king (mastermind funk guitarist/ songwriter/ producer).
The song was written for BTWN, where Bowie was reunited with NIle Rodgers, so it makes sense. Especially as there's another track off BTWN where Bowie is 'Looking For Lester (Bowie)'.
Maybe there was another track called 'Get Me The Crazy Pianist'.
Forgetting the title, the lyrics seem to suggest Bowie's farewell. Maybe that's why it was recorded 3 times (BTWN, Earthling & Reality), but Bowie only ever felt happy to release it when he was (subconciously?) ready to bow out.