Because even though they cover approximately the same amount of skin, they're completely different articles of clothing with very different connotations, and society views them in different ways. A bikini is intended to be worn in public, at least in the appropriate setting of a beach or pool. But undergarments are always intended to be worn beneath other clothing, and if a girl is in her undies it usually means she has taken her clothes off or is in the process of getting dressed, which are things that society sees as private and personal acts. The whole difference is whether or not they are meant to be seen. It may not make total sense, but who said humans were logical?
Bikinis are meant to be seen and usually you're in an environment where walking around half naked is normal. When someone walks in on you in just your bra and panties, you're not expecting them and so aren't mentally prepared for whoever it is to see you so undressed.
I wouldn't freak out, but I would be much more embarrassed than if I was in a bikini. I guess in a bikini everyone else around you is wearing one, and the material is different, but I don't have a good answer as to why, lol
im not that shy, so I usually don't freak out if someone walks in on me.
THANK YOU. I get that there's the whole "different setting" thing, but the logic just doesn't make sense. You wouldn't dream of wearing bikini around town, but on the beach it' all cool because everyone else does it.
It's partly about social mindset, but there is a physical reason as well. A bikini, being meant to be worn in public, "sticks" to the breast better. In a bikini, the girl can swim, play sports, or whatever without having any "wardrobe malfunctions" occur. In a bra, lean forward a little bit and hello nipples.