Saying that, I forgot my own jo injury!
I was moving to the outside (can't remember the technique) of a jo tsuki and the Uke kept following my turn no matter how far out or quickly I stepped. I decided to illustrate the fact that Uke was following me because he was getting used to where I was going to move, by turning the other way - this was just at the point when Uke realised he had been following my movement.
The obvious result was a jo in the ribs which, although it didn't hurt much at the time (though it gave an impressive thud) I had difficulty breathing the next day and could do no exercise for 6 weeks.
I was also hit on the knee once by a fragment of flying bokken, whilst in seiza - Tomita sensei was illustrating that everyone's boken was of very poor quality - a valuable lesson to us all.