Not sure what it was(never bothered telling me, I was a minor), pinched nerves or something in my back, when they found out what it was I remember them all acting shocked and asking how I was even able to stand without screaming.
The worst I've had for lingering pain is without a doubt burns, I work in fast food and am constantly burning myself. In one day I had hot(400F) oil spill on my right hand, covering about 60% of the palm and 3 of my fingers. Not 20 minutes later I spilled oil on the same hand. Incredibly unpleasant.
Another close tie for worst was stepping on some red hot coals, they stuck to the skin and kept burning, I was so desperate to get them off I was pulling them off with my fingers.
Then there are the minor things, soft tissue damage in the back hurts fairly bad, as do knee injuries(a snowmobile, me and a tree were involved, do the math).