I actually have a severely bruised cheekbone right now from an UAX flight the other day. The FA informed me (as she was walking to the back of the plane pre-takeoff) that my bag was not far enough under the seat. I bent down to fix that and she came walking back by rapidly and hit my shoulder and back at near full force, slamming my face into the seat back in front of me (the tray table part). My cheek is very sore to the touch and she wasn't very apologetic - also would not get me ice for it when I asked.