While my mother was staying with me over Christmas I took her to a favourite restaurant that I normally go to with friends. The owner was delighted to meet the mother of a regular, tactfully refrained from telling her how much I normally drink, and dispensed, along with a glass of port on the house, a well-worn compliment:
"Mama? I thought you were sisters!"
My mother laughed, taking the remark with a pinch of salt not needed for the food. I laughed too, but should I have? Perhaps he meant that I looked as old as my mother.
That the remark is always taken as a compliment to the mother rather than an insult to the daughter shows that neither believes it.