So this happened when I was in middle school, and I was 12, I believe.
For starters, I'm a cis girl, and around this time I'd just started going through puberty, and my chest got affected fast. 0-100 and all that. I'd never worn training bras before this point, so I was still getting into the habit of wearing bras daily.
Anyways, my school was small with only one class per grade, and they would frequently do this thing where students who'd not missed any homework assignments or gotten in trouble could have a reward every two or three months (pizza party, half of the day devoted to watching movies, little field days, etc). This particular time, we were all allowed to go outside into the large field/forest area and play a huge game of capture the flag.
Me and my small group of friends weren't too into the game, so instead we took to just wandering around talking. There was a creek that cut through the middle of the forest area behind the school, and we were walking alongside it. Cue us deciding to be stupid kids, and instead of keeping dry, we for some reason suddenly decided that we'd walk in it. Well, creeks can get get pretty damn muddy at the bottom, and my dumbass stepped into a deep spot, which made my foot get stuck. Of course I didn't realize, either, until I went to take a step and promptly fell forward, getting completely soaked in the process and losing my shoe to the mud pit I'd stepped in.
And remember how I said I was still getting used to wearing bras? Well, on a typical day I'd be wearing both a hoodie and a dark blue polo shirt (this school had uniforms) but on this field day, we could wear whatever we wanted, and I'm sure I don't have to tell you what happens when a girl gets wet in a white shirt.
So, I then had to walk, soaked wet in my see-through shirt and missing a shoe, past nearly the entire student body and up to a teacher. Then I had to pass through the school to wait in the front office until my parents could bring me dry clothes and a new pair of shoes. I guess I'm just thankful that most of the gross boys who'd make horrible comments about that sort of thing were troublemakers anyways and therefore not invited to that particular field day!
And I legitimately never forgot to wear a bra after this!