And it goes almost without saying, almost all involving young men.
I include this video in the hope it will inspire others to share tales of their worst wheeled equipment failures. For me it was a mountain bike, years ago, on a fire trail in the Santa Monica mountains. A property developer had tried to block access by piling dirt into berms about every fifty feet, but this made the route all the more spectacular on a bike (especially on the downhill). So it was, anyway, until the stem of the bike snapped and left me holding the handlebars with a confused expression on my face until the bike slammed into the cliff face to my left.
Good times, good times.