Man, what a bummer story. Yea, you shouldn't let your friends drive your stuff. I hate it when people ask to ride my bike. I go why not just ask me to ride my wife too sheesh. I hope he heals up ok.
dirtbiking when i was younger, my friend rode through a barbed wire fence that was hardly visible (at 50)... ripped his stomach open and everything was hanging out... disturbing to say the least, but he lived.
It's not a good idea to let a friend who is inexperienced with high performanced sport cars to get in the drivers seat of something like a vette. I have been in a few accidents that involved someone who was not familiar with the car or that level of power and ate shit around a corner. If you have a bad ass sports car -do not let your friends drive it - no matter how much they beg - they will just fuck up your car.
Sorry to read about your friend casavant. Best of luck to his recovery.