Never had a problem on a dirt bike. On my street bikes though, I have done what every other rider sooner or later has or will do - and thats the asphalt slide.
Early in my riding years, my state put in place a helmet law. I bought a quarter helmet, strapped it to my shoulder, and got pulled a half dozen times for it easy. Every time I got a ticket, fought it and won - the law said you had to wear a NCDOT helmet - it never said you had to wear it ON YOUR HEAD! To date, the law still reads the same. Now - I wouldnt ride without a full face helmet, along with leathers and most of the time, gauntlet gloves. I have the scars from not only a few asphalt slides, but I went into (and nearly all the way through) a car's back window once.
Its not that we are stupid when we are young, we just don't realize that it CAN happen to us.....
Ny parents always said I'd get myself killed - I always figured I would be immortal till something killed me outright. Thankfully that never happened.
Now as long as the chute doesn't tangle too awful bad next time I jump.....