Since it’s summer and this mindset begins to pop up more, let us clarify something.
Girls being upset over being seen in bra/panties but not bikinis is not a double standard.
If she’s in a bikini, it’s what she consciously chose to wear and be seen in, in a public space, and like any outfit she was prepared to be seen in it by other people.
If you’ve caught a girl in her underwear, however, you’re probably trespassing in her bedroom, bathroom, or other personal space, where she should be in privacy, and she has every right to be upset if that privacy is violated.
It’s not about what she’s wearing or what it is covering, but rather her privacy and consent to be seen in the first place. Please respect that.