This is not my experience at all. But I'm Finnish, and we treat nudity very differently to Americans, because sauna. We learn to be nude there from chilhood with our family. Mother, father, sisters and brothers go all together. In puberty it normally stops, and becomes gendered experience, until you have your own partner to go to sauna with. When I was in puberty, I had this female friend who went to sauna with her father at age of 15 and we thought it was beyond sick.

We don't understand the general hysteria about nipples. All finnish children learn to know how bodies look from very little. For us it is natural and it has always been like this, always. We have gone to sauna for thousands of years, and the whole country turning to christianity didn't do a shit for it.

None of my sexual partners have been shy about their bodies, all cis-males. I haven't been shy about my body when presenting as a female, though I didn't like it. We just aren't shy about our bodies. From the minute we've had sex together, we have gone sauna together and showered together and changed clothes in the same room.

So, this can be a cultural thing, or come from family background, or someone just is more guarded about their body. If they are thought home that being naked is private thing and shameful, they might have hard time to get over it with anyone.

Personally right now I'm in a situation where I would refuse to be naked with anyone because I'm trans and pre-everything. My dysphoria makes sure of it. I can't stand the idea of someone seeing my breast, no matter that quite the amount of men have seen them already during years. I didn't care then, I do care now because I know now I'm a man and men don't have THESE THINGS.