As a kid in family center pool changing rooms, there was one girl I awkwardly saw without clothes. But at that age, no breasts were developed. This meant nothing due to how young we were. It can be likened to how ER narrated the only time he saw a girl his own age naked—they were too young for it to matter.
Recently though, I saw a girl with an open zipper hoodie (you know, how they rest it on shoulders in the slutty way) and her tanktop essentially didn't cover her boobs at all while she was walking by. This was a strange sight because it was the cold months of autumn, and things that extreme aren't even seen that often in the summer. Memorable, but not sure if it counts.