In college I once decided to ride my mountain bike down the stairs of my townhouse and out the front door. There was about 4 feet floor between the bottom of the stairs and the door, then a straight drop to the sidewalk a little over a foot. Said sidewalk had a downward slope after about 4-5 feet of level.
I didn't have time to adjust my weight positioning in the transition from stairs (very steep) to floor to flying, and I exited the townhouse front door at approximately 1000mph with arms straight, legs bent, butt over rear wheel, chest/stomach over the seat. I promptly rotated about 120 degrees to the rear, and barely made contact with the rear wheel to the pavement before going all the way over to land on my butt, back, head, shoulders, etc.
Cracked my helmet. Got back up and did it again but did not crash