You know the rule, anyone can tell bra size (chest and cup) from 100 feet away in dim light, even if the wearer is male. A favorite of many authors, especially those who appear to be just starting out. When I'm reading I take it as a negative, although I've read many stories worth the read despite naming the size.
When, if ever, is it useful / effective / advances the story / describes character [insert here any other writerly term you wish] to provide the bra size---34B, 44DDD, etc.?
Having the protagonist notice a bra in the laundry and pick it up to read the label doesn't count, unless the action does one of those things listed above.
I can't think of a good reason, but that's why I'm asking.
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