Some men don't need an excuse to whack off in public. Many works we consider masterpieces were originally considered at least titillating or shocking, if not obscene; Edouard Manet's "Olympia" was literally scandalous in 1865, and was intended to be. John Singer Sargent had to repaint a dress strap on Madame Gautrau's portrait; it had to be exhibited as "Madame X" in order not to raise a scandal about the real model. I am sure you know these paintings; they were not always seen through 21st century eyes.
Many paintings of women "en dashibille" were only exhibited in bars and men's clubs where women would not see them. I cannot swear as to what men did in front of them, but I suppose the floors were in questionable condition for numerous reasons.
I remember the early days of Playboy, when the models were somewhat orange in color, airbrushed to the point of unreality, and showed very little compared to today. What was "naughty" in the fifties and sixties is humorous today.