I am not sure if has more to do with the underwear, as opposed to the situation. Sure, a lot of underwear can be see through, which can affect things, but if at the beach, being seen in underwear vs bikini isn't a huge deal, at least to me. I will say, underwear isn't really made for getting submerged in water, so it can get more see through as well. I have been in situations at a pool where swimming in underwear did not make me uncomfortable. Now, if someone walks in on me in my underwear then yes I might be uncomfortable, but this is because I am not in a situation where I am expecting to be seen in minimal clothes, and not because it is specifically undewear vs a bikini that I am wearing. I am not sure if that makes sense or not.
I worked in a dorm and some of those co-eds liked to be seen in their underwear, strutting around in matching lingerie and trying to tease the maintenance men working in public areas.
I can relate and not relate. I have 3 sisters and zillions of girl cousins I grew up with. I currently live in a sorority. When hanging around together casually and there are no boys around we frequently wear tank tops or tee shirts along with panties.
Boys seeing girls in their panties frequently give it a sexual or erotic overtone. It's most likely the reason girls avoid that circumstance in the presence of other males. At the beach, a bikini, which can look exactly like a panty, now has a social context that supposedly defuses the sexual overtone. Thus, girls are more likely to feel more comfortable in such environs.
Consent. Some people have seen me naked. But just because some people have doesn't mean all people have. Just because bikinis exist doesn't mean I need randos seeing me in my underthings. I know you think you're being witty but it's frankly frightening you don't understand this.
