Got a couple that rank equally high for me.
While skateboarding, I had a ghetto-rigged grind rail that consisted of a 4x4 post about 10 feet long, with some nylon siding to give ya somethin' to slide on. The board I was usin' was a Powell that had been found in a resale shop, and was missin' most of it's nose and tail.
So, I go up for a board slide (back side, 'cause they're easier), I ollie on, my front foot misses the nose, 'cause the board's FRICKIN' SHORT, but my back foot catches the tail just fine. Ordinarily, this don't pose much a problem, but this time I had a GREAT pivot point for the board so that as I landed, I snapped the tail, the pivot point sent it STRAIGHT into my balls.
I was on the ground for awhile. My little brother was too, but that's only 'cause he was laughin' so hard.
The other one was also a skating related one. Only this time it's not the board what was short, was the rail. I go up, try and 5050, realise this ain't workin', so I jump off, step on the end of the rail, pop it up vertical, I catch the rail right in the middle of my upper arm. It misses by bicep, hits bone instead.
One of those pains that alternates 'tween laughin' hysterically, and cryin' the same it hurts so bad. Bruised the bone somethin' fierce, maybe chipped it, otherwise, I got tough bones.
Got a non-skatin' related one, but that's not entirely inanimate, since it was my brother who was wieldin' the bokken what snapped on my forearm.
Good times, aye?