Though this did not happen to me I witnessed a really dumb accident.
When I was a kid my buddy was going downhill and only hit the front brake on his mountain bike. Well the rear wheel popped up a little bit and he thought this was pretty cool...
Well then the brilliant idea popped into his head that if he went really fast and hit the brake really hard he could get the rear wheel to pop up much higher. As you can imagine his hypothesis was quite correct.
He proceeded to go further go up the hill and really let loose. As he rapidly approached he gave that front brake all the strength he could muster. At which point the rear end with him quickly arced through the air. As he went face first towards the ground he somehow managed to save his head from hitting the ground by stopping the fall with his hands in a push up position, briefly anyways. A moment later the bike finished its flip by hitting him in the back of the head forcing his face into the asphalt.
He never tried that trick again.
Hmm, can relate - was cycling right next to Blackpool Sands beach
(going towards Dartmouth if you know it)
going down a 12% twisting road and got a bit too much speed up, then realized the bottom corner was a 90 degree right turn, with a pointed (jagged sharp stone finished) 4 foot wall at the end of the downhill part, with a good few feet drop to a stony brook behind it. Used the back brake, the backend slid out, switched to front brakes, and to the bemusment of the cars behind me, proceeded to go down the latter half of the hill on my front wheel, before going over the handlebars and hitting the wall - all the more fun for being in BB cleats to the pedals at the time. One broken bone and a trip to Dartmouth casualty later...
Sympathy for the OP - had a friend lose his front wheel. fork dug in, he went flying. Better than a full force impact to the nuts though...