I'm going to treat anything where I had memory loss or an obvious concussion as a head injury:
~2, fell off a counter onto my head, had a concussion and did the whole projectile vomiting thing.
~6, running, tripped and fell, top right of my forehead hit the corner of a concrete fireplace ledge. I actually don't remember this one, but I'm told the story a lot.
~10, watching for tornadoes, running barefoot on a concrete garage floor, charlie browned right on the back of my head. Several stitches for that one.
~13, walked into a pole because I'm retarded. Was walking along, next thing I knew I was on the ground, thought someone had hit me. Figured out a few seconds later I must have walked into the pole.
16, ran into a fire hydrant with my car, once again because I'm retarded. Was out cold from the airbag for about a minute, also bit clean through my lip, have a nice scar still from that.
So now you guys know why I go around mumbling 'INFJs are gross' all the time, one too many shots to the head.