Here's mine:
Riding along off road, I had to ride over approximately 4 little branches (maybe 4cm in diameter) spaced about 20cm apart (some of you might know - near the end of 'Second Coming', after the gravelly section and between two short descents). I must have thought my bike would just go straight over them, and didn't lift my front wheel and went over the handlebars. The worst bit is that I managed to wedge my legs under the handlebars somehow and the bike literally pinned me down upside down (ie. seat was in the middle of my back, wheels in the air). Lucky I was riding with a couple of friends and they were able to pull the bike off me so I could get up. I sometimes wonder how I would have managed to get up, had I been riding on my own. I probably would have waited until someone rode past...
Of course, I've had a couple of stacks trying to trackstand at traffic lights too, but I deal with that by kidding myself that it happens to everyone.