I've just had a flashback:
Noel Coward, "Private Lives". Saw a production years ago so I can't be totally sure, but the somewhat middleaged heroine's name was
Amanda, and the younger woman, soon after they meet, says "I shall call you
Mandy!", to which
Amanda languidly replies something like "Yes, I suppose you will" in a dazzling display of ageist and classist superiority.
Something similar in one of the late
Margery Allingham novels.
So, in general,
Amanda for the toffs and
Mandy for the rest of us?