… Do we, Kat? I mean, pear-shaped we do say, yes, and the body shape is old (1815); the “things went wrong” meaning is much later, and may (may) be unrelated: Pear-shaped.
But banana-shaped? I haven’t heard that. I have heard “flat as a pancake” instead, and pancakes aren’t fruit. Apple shaped? I haven’t heard that either. I have heard hourglass-figure, but hourglasses are also not a fruit.
And of course there’s real cultural difference at play here. Korea has the whole peculiar trend of using letters of the Latin alphabet to classify body shapes: S-Line, V-Line, and 19 More Korean Body Lines
Two things going on here. The impetus to classify female body types is tied up with the… dare I say objectification? of women. Commodification, certainly. Women are evaluated for desirability according to specific ideals of body shape, and are therefore classified according to how they meet or fail to meet those ideals of body shape.
Why fruit? Well, why letters of the alphabet? Accessible, recognisable shapes, preferably like Kathleen Grace said with connotations of sensuality (which fruit have)—although that is not mandatory, as Korea shows (and so do hourglasses).