Are only
women doing it? Max Cryer explains:
The genesis of ["everybody's doing it"] can be traced to a Mozart opera of 1790, commissioned by Emperor Joseph II of the Holy Roman Empire and said to be based on a much gossiped about real-life incident in Vienna. Mozart's librettist Lorenzo da Ponte entitled the story Cosí Fan Tutte — which translates as 'Everybody's doing it' (though purists will point out that 'tutte' can be seen as the feminine of 'tutti', and thus only women are 'doing it').
(
Who Said That First?: The Curious Origins of Common Words and Phrases, 2012)
