Admittedly not bizarre, but the ground.
Halcyon BMX days, when an exaggerated sense of ability met an equally exaggerated sense of uninjurability, and led me to believe I could move at speed on only my front wheel. Essentially, ramp up to warp factor ten and then slam the front brakes to kick the back end up into the air and keep your entire body over the front wheel to see how long you can roll along on the front wheel alone.
The answer was "not long".
Especially if you right foot slips off the pedal and into the front wheel causing a rapid deceleration and sudden approach of tarmac. After my chin had worn a grove in the tarmac sliding to a halt I did the usual damage report. Seemed good. I had survived with minimal damage. Didn't even hurt that much.
Unfortunately, I hadn't released the back end of the bike was still wavering above me, like the Sword (well, Hammer) of Damocles. Over it toppled, the bike saddle falling like hammer on the back of head, replanting my face in the pavement. Cue re-evaluation of that damage report.