Some of the most serious injuries are caused by negligent entrustment of dangerous devices or vehicles. Consider the following situation which is very similar to the case a recently handled: A, B, and C are sitting at A's home and having drinks. After a few drinks, A gives B keys to his A's ATV, and B decides to take a ride. B runs the vehicle into the tree. B's body is thrown of the vehicle and against the tree. B suffers debilitating injury and ends up being partially paralyzed.

Although one could argue that ethically B is just as at fault of riding ATV drunk as A for letting him borrow the vehicle, A will likely be liable for B's injuries and damages under the negligent entrustment negligence theory, because A knew or should have known that B was under the influence and was unable to safely operate the vehicle.   

In that case, the ATV was not insured (as off-road vehicles do not have to be insured in California). If A is a homeowner, his homeowner's insurance policy will likely cover the injuries caused through the use of vehicle kept on the insured property.