Injuries you should never get. because of the pain factor. not because of what the injury might do to you, or prevent you from doing whatever you want to do.

pain level according to injury. 1 being the most painful. note that this is according to what i think and deduce from facial expressions of other people sustaining these injuries. not that i have experienced these injuries.

3. severe lacerations (google it if you dont know what it is. google the word laceration in google images, dont vomit over your keyboard.)
2. broken bones (ribcage, ankles, joint areas are very painful, as well as shin and other long bones. back bone doesn't count, because then, you can't feel pain anymore.)
1. burns. (3rd degree burns are the worst. arghh, just thinking of this gives me pain...)

till then, stay safe...