Worst I've had was camping on a boy scout trip on a flat spot that turned out to be the middle of a gully when it rained. Soaked my tent and sleeping bag. Fortunately, I had dry clothes to change into when my assistant scoutmaster noticed I was going hypothermic!

We used to drive through Spring City, TN fairly frequently when I was younger. There's a monument to the scouts who were killed in a flash flood, and Dad pointed out the monument and re-told their story almost every time we passed it.