Definition of It boy in US English:

It boy

noun

US
informal
  • Originally: a sexually attractive man, especially a film star; (now also) a man who is very famous, fashionable, or successful at a particular time.

Origin

1920s; earliest use found in The Chicago Tribune. From it + boy, probably after It girl.

Pronunciation

It boy

/ˈɪt bɔɪ/