There Is the Brunette (1958)

Germain Vignon is a used car dealer whose eloquence is such that he could sell the lousiest banger to a guy that does not even have a driver's license. He is not bad either at chatting up girls. Indeed, since his blonde wife left him, Germain has seduced no fewer than four brunettes. And as, besides being a ladies'man, he has a heart of gold, Germain is unable to break up with any of them, hence a complicated sentimental life. But this delicate balance is threatened the day an outraged stranger comes to him and orders him to leave his wife alone. One small problem is that the man has forgotten to specify the name of the lady in question. So, which of his four mistresses - Christine, Sophie, Anne-Marie or Sonia - should he leave?