I once hit my head on the lower section of some stairs... but had no permanent injury as a result...
Just once? Amateur!
I've hit my head on the lower sections of stairs, slanted attic ceilings, the corner of a cupboard (several times), open cupboard doors (also several times), a low living room ceiling (I was jumping up and down), a chandelier, my brother's head (he's got a skull like a Pachycephalosaurus), the headstand of my bed, the wall of my room (since I got rid of the headstand, that's what I've been hitting my head on when I wake up in the morning
), and the inside of an inverted glass bubble looking into a fish tank at an aquarium, just to name a few things. (No wonder I have memory problems today...
:)
Hehe, here's somethin' we share in common. Also, I've hit my head on a hanging flower basket (my mother happened to be with me and laughed her a** off, especially when I said, "I just took a geranium to the cranium!"

), an iron plant hook sticking out from the fence (I was running by the fence and not paying attention

), an alarm clock, a coffee table, a sofa (I have a dent in my skull where I hit my head. Good thing it's not visible), a window, the pavement, ice, a locker door, and many more things than I can keep track of

. A funny one was when I jumped to get into a Ford Expedition (I'm short) and I jumped a little too high and smacked my head

. Oh, and I once got pegged in the head with a glass cieling light cover. A relative tossed it to me when I was not paying attention, thinking I knew it was coming

.