when i was 10 i was training fro a tennis tournament took a serve and partially tore a ligament in my wrist.
that hurt alot. I have also torn my gastronemeus in an 800m race then foolishly finished the race rather than stopping making it worse
then my favourtie but the least painful happened to my co-coach. we were messing around in the sports hall waiting for the kids to turn up and he opened the fire door and said he reckons he could nail a jumper from inside the door. he jumped and smashed his had on the doorframe which was metal. that was funny but hurt him none the less