Well, my favorite show mishap involved my sister and her little Arabian, Jessa. Jessa loved to jump, but had horrible form. She would fly around the arena and fling herself at the fences, shoulder first, forelegs dangling behind her, and then scramble mid-air to pull her legs over and get her landing gear down in time to avoid a crash. They were in a class with jumps about two feet high, and Jessa was flying down a line of jumps. They got to the first turn, but Jessa just kept going, right over the end fence, through the scattering spectators, over the hill and out of sight.
The weirdest thing I have seen training was at a dressage clinic with a very well-known instructor. Theinstructor wasin the middle, teaching the rider, but also talking to the observers. The student was very experienced, like PSG, and was on a magnificent horse. At one point during his session, he was directed to ride sitting trot to the corner and then do an extended trot across the diagonal. He did this, really flying across the ring with the instructor talking to the crowd about his trot, when the guy slammed into the far corner wall, still at a full extended trot.
When the astonished instructor asked why he did that, the rider said that nobody had told him to turn.