I've been fairly lucky as far as injuries go. The two ones I can think of that had the worst potential to leave a long-term injury would have been slipping backwards while going down a stairwell and smashing my head on the step behind me, and getting a small piece of sand in my eye. As silly as the second one sounds, it was actually large enough to cause permanent damage to the eye if it hadn't been removed.
However, neither were very painful, in the former case probably because of shock. The most PAINFUL injury I've ever had is accidentally closing a car door while my hand was still inside its arc.