Lady Astor to Churchill: "If you were my husband, I'd put arsenic in your coffee."
Churchill: "Madam, if I were your husband, I'd drink it!"
But she also had the better of Churchill on one occasion:
Lady Astor was giving a costume ball and Winston Churchill asked her what disguise she would recommend for him. She replied, 'Why don't you come sober, Mr Prime Minister?
- Source: Nancy Astor, Viscountess Astor, Wikipedia