Okay, just to add a little bit of context, the one who posted about not wanting to wear her bra in front of the doctor, she believed he was a creepy perv. What that had to do with her bra, I would have to imagine the bra sexualized her body in some way.
Just as the jockstrap did for me. It looked and felt like sexy male lingerie from the time I put it on, And at the time I was only beginning to have sexual feelings. So maybe she felt the bra sexualized her body, as she wrote, "but to me it was worse if he saw my bra vs my tiny just-starting to develop breasts". Where being nude is nothing but a plain body with nothing special to look at.
So a bra might trigger some early sexual feelings, which comes along with hang ups, being uptight about things, and just a lot of awkwardness with coming of age, that I'm sure those who tended to be more shy became more self conscious, feeling a bra strapped onto them. The feeling that their bodies were developing to the point of needing this undergarment, and now someone who's practically a stranger, a doctor, will see them in their undergarment, which they are generally not exposed to the public while wearing it. And the lack of experience of someone seeing you in something you may not even be used to wearing.
I realize many folks can't see what the big deal is. For the guys who thought it was nothing to walk around in gym locker rooms in their jockstraps, and for their finer counterparts to be among each other in their bras. But then there are some of us who may have been more shy and perhaps sheltered, where there was a point where it may have been more dramatic.