Are you responsible if someone borrows your car without permission and gets in an accident?

The owner's insurance will pay if he has collision coverage. It Doesn't matter who was driving. the owner will have to pay the collision deductible, unless he wants to press charges against his buddy for "stealing" the car in which case the owner will have to pay the Comprehensive deductible. If the owner has neither collision nor comprehensive, then the owner is out of luck. The buddy's (who borrowed without permission) insurance company is not responsible for anything. They were not insuring that vehicle only his liability (damage he causes to people and vehicles that he hits but is not occupying)