Poorly Fitted or X-Rated Bottoms 

No butts about it. Too little, too late. It's difficult to think of anything more unsettling at the beach than seeing women with generous derrières prancing around in string bikinis. Just because baby got back doesn't mean everybody needs to see it. 

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No matter the composition of your can, your bathing suit shouldn't be X-rated. In other words, all of your assets don't have to be on display. Dial it down, at least when you're out and about. 

Of course, you also want to avoid the adverse effect, which is excessive coverage. If your bottom is too large or too loose, you might get the saggy diaper effect or find yourself always adjusting wedgies, which can be equally offensive. (Not exactly a very ladylike gesture to be caught doing in public.)