From Italianbimbo("a child, a male baby"), variant of bambino("child"). Originated in Italian American theater, attested 1919, as "stupid, inconsequential man", by 1920 developed sense of "floozie, attractive and stupid woman". Popularized in 1920s by Jack Conway of entertainment magazine Variety, who also popularized baloney("nonsense") and palooka("large stupid man"). Revived in popularity in 1980s US political sex scandals.
And one had to remember that most of the bimbos to whom Roberta Wickham had been giving the bird through the years had been of the huntin', shootin' and fishin' type, fellows who had more or less shot their bolt after saying 'Eh, what?' and slapping their leg with a hunting crop.