I don’t think I had an especially sheltered upbringing, but I don’t quite understand a reference in John Brophy’s The Bitter End (1930). Donald, the hero, is strongly attracted to Celia, an upper-class WAAC, until one day she makes a gesture:
There was current at the time a slang phrase used to express intense pleasure and triumph and accompanied by a gesture of the fingers. Everyone not too genteel used it, in this sense, but among coarser and more knowing people it passed as a euphemism for the sexual act performed illicitly.
Celia makes the gesture, in the company of soldiers, presumably in the innocent sense, and Donald is overcome by shame and embarrassment:
He lost all balance and control; hot surges of shame and rage and grief shook through him. He hurried blindly out of the room.
Brophy editorialises that ‘A saner or older man would never have made Donald’s mistake.’
The embarrassing incident is convincingly described – so convincingly that I bet it is autobiography – but what I’m not sure about is – What exactly was the gesture? Any suggestions will be gratefully received.