Bruising can actually turn into a serious problem if not treated properly, I agree little cuts and bumps aren't true injuries, but if you are repetitively hitting the same bruise and it doesn't heal properly, it could turn into Myositis Ossificans - bone growth in the muscle bruised.
"Pretty sure they can stop 35 suburban white kids in tall tees and jiberish." -papa_lanks
"hold on. "checks pulse"
nope. im definitely alive you're just an idiot." -Shark.Pen
Opinions are like nipples, everybody has one. Some have firm points, others are barely discernible through layers, and some are displayed at every opportunity regardless of whether the audience has stated "I am interested in your nipples" or not - David Thorne
I think the most common injury is hurt feeling though. Honestly that's probably the worst too. Broken bones and other injuries hurt, but you go to the hospital and they fix them. Hurt feelings might not seem that bad but you could be going to therapy for the rest of your life trying to shake the shame.