When we first met my wife wore what I would consider "normal" bikini bottoms, covering approximately half her ass.
Over time I convinced her to buy bikini bottoms that cover less. Way less
For some time she had some modest bikini tops and bottoms to wear around friends and the more cheeky sexy ones for when there was noone there we knew. But she didn't really care if a lot of strangers could see her.
At waterparks she would often wear string bikinis, the teenagers waiting in line behind us really enjoyed the sight.
But she refused to take the padding out of her bikinis because she was afraid her nipples were visible. Recently I managed to convince her to take them out.
She doesn't like the feeling of wet bikini tops on her tits, when possible (beach, lake, but not public pools or around most of our friends) she goes topless. But where a top is mandatory I convinced her to take the padding out for the bikini to dry faster. But she always put it back in when dry.
One day she got a new bikini, cheeky bra style with a string bottom. The bikini is nice but the padding is really cheap and has a weird shape. She realized herself that it looks way better without the padding, so he removed it.
But the fabric is also really thin. When dry and her nipples are not fully hard they are visible if you pay attention, but when the bikini is wet and her nipples are hard they are very apparent.
But she likes the bikini a lot because "it fits perfectly with my... *all kinds of stuff*" so she wears it often, also around friends.
Apparently she got used to having her nipples on display, because she now doesn't put the paddings back into the other bikinis after washing them. I really enjoy it when our friends look at her tits and her nipples poking through the thin fabric