I always like to think back to a great moment of accidental / unaware nudity concerning my girlfriend’s little sis. My gf was still living at home with her mom and her younger sister at the time. I had only stayed overnight with them on weekends a few times before. On Sunday mornings we would have breakfast in their kitchen all together. Her sister usually got herself out of bed a little later and would typically, still half-asleep, come stumbling into the kitchen for a cup of coffee and sit down with the rest of us. On that very morning she had just come out of bed again, still wearing her red T-shirt from the night before and some loose-fitting satin panties (like boxers but especially made for women; a bit like hot pants-style with intentionally short legs, but not as tight). She helped herself to a cup of coffee and sat down sideways to me on the bench seat.
At that time she was arguing a lot with her mom about people she wasn’t supposed to hang out with – not at least her first boyfriend, being 11 years older than herself.

So it didn’t take long until her mom would begin quizzing her about where she had been the night before and stuff like that. While engaging in the first discussion of the day with her mom, she was rising up her left knee, putting her foot up on the bench and then placing her elbow on her left knee. Her tiny naked feet looked pretty sweet by the way, but much more mind-blowing was the view her new seating position suddenly allowed me. Her thin bent legs were leaving a large gap between her thighs and her loose, slightly oversized panties. It literally took my breath away as I realized that the little fur that I was seeing down there belonged to her vagina and that her position allowed me a perfect side view on her nude pussy lips. The most thrilling thing about the situation was that, being distracted by the conversation with her mom, she was sitting like that for minutes, completely unaware she was just showing me her pink bits. If she knew she would have sunk into the earth out of shame! My girlfriend was sitting at the opposite side of the table and had no clue of how her little sister was just freaking me out.
Back in my girlfriend’s room a little later, I was still so horny that I let her know I was in the mood for getting it on. She somehow found it funny that the “family breakfast” had apparently made me horny and kept joking about it for a while, but was eventually giving me a quick handjob while we could still hear her sister and mom quarrelling with each other. I’ve never told her why I needed her hand so badly that morning… but when I see her sister I always remember the look of her pink bits and feel a little privileged for being one of the first guys to have ever seen her pussy.
I’ve really liked her since that day. As long as my girlfriend was living at home - with the women’s unattended laundry always in reach - I quite regularly took the chance to jerk off while sniffing some used panties of her sister … unfortunately, I haven’t had the chance for years, but I still know how her pussy smells and will (hopefully) never forget her aromatic odor.