When I as in 8th grade, in our class we were rehearsing some folkloric dances, so all my girl classmates were wearing this long wide skirts with colored stripes.
Something nice about those days, is that the dances normally involve the women spinning around. That make their skirt raise really high. It was usual for us to take great peeks of their panties in those spinnings (nowadays they don't grant us those free views, and women in folkloric dances wear athletic pants, or shorts under the skirt).
Well, that year, a few of us had to go to the library. For some reason, I was the one man that had to go. While we were there, my teacher sent me outside to do something (I just can't remember what). The funny thing was that I took me less time to came back then what they spected. So, when I got back the teacher was talking to the girls, one of them (a skinny brunette called Milagros, Miracles in English) was playing with the bottom of her skirt, slowly swinging it from one side to the other, and from front to back. Obviously she didn't realize I had return, because without any care, in one of those swings she just raised her skirt all the way up, giving me a full view of her silk white panties.
I stood in the entrance door for a few seconds, and wasn't until she lowered her skirt that I walk in, pretending that I hadn't seen a thing.