Having my coccyx bone broken by a spinning back kick (we went for them at the same time; his hit first). Very spooky, as my legs went numb from the impact, then a luxurious coating of ARGH as the fire and needles set in. And of course, sitting and going to the bathroom was a thrilling experience for the next 5 weeks or so.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin