My sister is quite a bit older than me, 10 years to be exact so she was wearing thongs when I was like a baby hahaha. Pretty sure she was wearing thongs around 12 years old cause I saw an old photo album a few years back and it was her 13th birthday and she had a pink whaletail showing above her jeans in a few photos.
Needless to say I was exposed to whaletails and thong slips early on hahaha
My first vivd memory though was when I was 9 or 10 so she would have been 19 or 20. My sister was driving us to the amusement park. Her friend was in the passenger seat and I was in the back. Her friend just got her license so when we got to a red light, she asked if she could drive the rest of the way. So her friend gets out and runs around the outside of the car to get to the drivers side and my sister undoes her seat belt and tries to slide over to the passenger seat while staying in the car.
She was wearing a white t-shirt and black yoga pants. And holy fuck did those yoga pants slide right off her ass
As she was dangling her ass between the two seats trying to sit down on the passenger side, I saw like 7 inches of her light pink thong. It wasn't pulled up high either, I saw about an inch of butt crack so basically her entire ass cheeks were out. She got super embarrassed and asked me if I saw anything.
Her friend saw my sisters entire ass out as she was getting into the driver side and burst out laughing. That was all at the same time as my sister had asked me that question. I was so astounded by what i just saw that i played dumb and said "what are you talking about?"
Honestly this was a big learning lesson for me to not tell a girl her thong is showing. I thing that since I played it cool in the car, for the next 4 or so hours at the amusement park she let her thong show the entire time! she was bending to get on and off of the rides and I was just entranced by it hahaha. I think it was one of those moments that made me realize that I fucking love thongs hahaha