Horrible is when "someone else" has to pay the price by subsidizing the medical care of a person who doesn't understand inertia. Experiencing the consequences of behavior should be educational. If experience didn't alter future behavior, that would be horrible. .
A passenger with their feet on top of the dash would be injured in a frontal collision even with no airbag. As an experiment in my garage, I tried putting my feet up there and found that it was very difficult to do while wearing the seat belt. Without it, a passenger would become a projectile. In a frontal collision, if the windshield restrained their feet, the ankles being over-extended, the face thrust into knees, the butt sliding forward and dropping down, could result in all the described injuries. The degree would depend only on speed.