My best story was from the first time I saw a thong IRL, which was in upper elementary school (8th grade). So at age 14, both for me and the girl. She was one the cutest girls in class, and keep in mind back then it wasn't that common to see thongs. Also, there was no internet as we know it today. Sights of thongs were rare.
This day we were in class and she sat in the front row, I sat behind her to the right. Her position was so that she had her legs stretched far in front of her, and then she started to slide her bum across the chair a bit in order to sit more upright. A panty was showing, but you could only see bare skin between her panty an her jeans at the hips. However, this was enough to get the boys in class to start whispering. I didn't say anything, because I was extremely shy back then, but I could hear guys around me asking each other if that could be a thong.
Then, after several minutes, she slid her bum more across the chair, which made her pants "get stuck" between her bum and the chair, so that more panty was shown. And this time you could see it was a thong. Not much skin was shown, but enough. I specifically remember having to take a deep breath because my heart was pounding fast and heavy. First thong IRL I ever saw, so I remember it very clearly.
Several guys in class made hand gestures to each other, drawing the shape of a thong (so they didn't have to speak loudly). Later, during the same class, a guy loudly expressed, as a context sensitive reply to something the teacher said "Imagine Helene walking around in just her thong at home". I can't remember what the teacher said to trigger this comment, though. But the teacher got obviously a bit taken by surprise I remember. I mean yeah, she was 14, but some girls pretty much have adult bodies at that age, and it would be a complete lie to say that teacher didn't find the looks of these girls to be sexy.
END
Then I remember another story that wasn't thong related. In the same elementary school, three guys picked up a girl, holding her like a clothesline. One held her hands and one held her feet. The third guy slapped her bum and, while giggling, said "look how it jiggles". Several other girls who were nearby giggled at this comment. The girl getting slapped wasn't overweight by any means, but her butt wasn't firm I guess.
It was just such a bizarre event and it only happened once. This was also before feminism, so both the girls and guys just laughed it off.