"Mad About The Boy" has been covered by many artists – most of them women for obvious reasons - but the definitive recording is probably that made by Dinah Washington. There remains some speculation about the identity of the boy in question; one answer is that it was anyone you wanted it to be, a composite character of the leading men of the day, perhaps. There is though another possibility.
The lyrics refer to the boy having "a gay appeal"; although the word gay
did not become synonymous with homosexual for another three decades and more, according to the Encyclopedia Of Homosexuality
, the phrase "gay cat" meaning "a homosexual boy" first appeared in print in 1933; and had obviously been in use some time before that. Noël Coward was homosexual, and had a wicked sense of humour, so it is quite likely that the song's title was an in-joke.
Homosexuality between consenting adults was illegal in Britain up until the Wolfenden reforms of the mid 1960s, but even then Coward did not "come out", and regarded the "gay scene" with contempt.