Breakfast at Tiffany’s. The first revelation was that the romantic leads were pretty much BOTH prostitutes. And then that horrendous turn by Mickey Rooney as a Japanese man!

…m.wikipedia.org/…/Breakfast_at_Tiffany's_(film)

Also the musical Gigi. More prostitution, this time with a mother grooming her daughter to enter the profession, while her client Maurice Chevalier croons “Thank heavens for little girls.”

en.m.wikipedia.org/wiki/Gigi_(1958_film)

I saw both these films as a child and had no clue.