When is a borrowed car a stolen car?
Answer: when the owner says so.
If the rental car is overdue the rental company makes a call to the police and tells them it's stolen. A rental car kept beyond the term of your rental agreement becomes a stolen car. Congratulations, you are now driving a stolen car.
If your girlfriend, neighbor, friend, or family member wants the car back and calls the police and declares it stolen…….Bingo…. you now are driving a stolen vehicle.
Avoid this problem by respecting the owner’s wishes and keep in regular contact with the owner. Call the rental car company if you need to extend the agreed return date.