In the dojo: (no padding/protective gear)
Worst --> Full force finger jab to the front of my throat, right in the center, just above the collar bone. Couldn't breath for about 20 seconds, and had a hard time swallowing anything for a week. God that hurt. Getting hit in the throat is a very unique pain that I hope none of you will ever experience.
A few others that weren't as bad...
I was sparring this guy, and we both went for a round kick to the head at the same time. Knee to knee hit, wasn't pretty.
First month of martial arts some moron, who had no control, put me in a wrist lock, and instead of going through the movements of a take down, he went all out. Tore a tendon and a few ligaments on the left side of my left wrist. Happened 6 years ago and its
still a little tender.
Full force heel kick to the side of my head.
Jong bong (boa staff) to the eyebrow. Some students need to work on their grip.
Grappling with a ground fighting instructor/US Special Forces guy. He got me in a strangle hold, but I had some leverage with my hand, so instead of choking me out he pulled my head back to the side. Heard my spine pop all the way up, and I couldn't turn my head left for two days.
Aside from rolling my ankle while running a few times, those are a some of the worst.
Edit: Learning (to put it lightly) how to do the splits. Longest 30 seconds I'll ever know.