Literally translates to "find the woman". Used facetiously to suggest that when a man does something stupid, a woman was probably involved. This is not to indicate that it's the woman's fault, but that the man is trying to garner a woman's favour, or to cover up his infidelity.
Did you hear? All of a sudden Bill says he's morally opposed to porn.
Yeah right. Cherchez la femme.
Yeah, I think he's trying to impress the girl at Starbucks.