Accidentally biting your own tongue/cheek.
Catching yourself in a zip, (if you know what I mean). Going to hospital and having a beaming matron say, "This won't hurt." a second before proceeding to rip apart the zip. Ruined a good pair of trousers and sprayed blood up the wall and onto the ceiling.
Swollowing break fluid. It has no colour, no smell, no taste and nothing happens for about 15mins. Then all hell breaks loose and you can't get away from the burning pain in your throat and stomach. On the bright side, the pain eases after a couple of hours. Even worse than drinking bleach, (yes, I accidentally drank bleach when I was about nine.) I say about 9, as I don't remember the age, only the pain.
TGB