What incident did you witness and at the time made you truly laugh out loud but on later reflection it wasn't funny?

There was a boy in the year below me at school who was, quite clearly in retrospect, profoundly autistic. He was fervently into Pokémon and Star Wars, used to wear a cape to school, barely spoke save for a few rehearsed words in a strange, high-pitched accent. By all accounts he was clever enough, but completely in his own world. You get the picture, which is why I feel bad for laughing. I was walking home from school one day in the winter - important for context, as there was a lot of snow and ice out. I had crossed a bridge that had steps and a ramp leading down from it, with a very steep grass slope separating the two. I'd just reached the bottom of the steps when I saw this boy approaching the top on his bike. He obviously realises that the ramp is covered in ice, so he decides to try and cycle down the steep grass slope. He sets off and immediately starts flying down it at a rate of knots. He clearly panics and yanks the back brake on, consequently taking a tank-slapper and sliding on his arse the rest of the way down. Luckily because of the snow, he and the bike are both OK. He dusts himself off and goes to pick up the bike, which is now facing horizontally against this steep slope. He sits on it, but as soon as he puts his feet on the pedals, he immediately falls in this cartoonish, slow-motion fashion back onto the grass. If you can imagine the "cardboard cutout falling over in a cartoon" trope, that's exactly what it looked like. But what really made me laugh was the elderly dog walker who happened upon this, who stopped, turned to me with a confused expression and mouthed: "what on earth?". Disclaimer that wasn't hurt at all, and did manage to get himself home without further incident. But of course I should have tried to help him, or at least discourage him from trying to cycle down a snowy grass hill!