My most recent was last night on a group ride. We were all jumping the transition from scarified road (where it's all scraped up ready for new asphalt) to smooth pavement, and I landed my rear wheel smack down on the edge and blew my tire. D'oh! Trying to fix the flat quickly, I changed tubes, inflated with a c02 cartride and it blew out through a hole I didn't notice. D'oh! Thankfully I carry tire boots.

Another funny one was when my buddy left his helmet at the observation tower in Shenipsit State Forest and we both didn't notice until we had descended the park road to the bottom.