Camped the other side of a wall from a rotting cow. Wondered what the smell was. Found out in the morning.
Friend left with the flysheet in his pack, and the rest of us had to sit out a rainy few hours in the Cwm Bychan car park in a leaky inner, with no food, waiting for my Dad to come back and fit the rest of us in his car (about 3 decades ago, and I still remember the misery).
Inadvertently pitched on a human turd. That was the worst.