He can report it, that’s just a phone call, but if the car is truly yours, he’d be making a criminal complaint and if he does that and knows it’s not true, that’s a crime in itself. If he does report it and you’re driving it, you might get pulled over, and the police may impound the car if you’re not on the title or registration at all. They could also get everyone involved together and go from there, but don’t always want to get personally involved. If you’ve paid him for the car, you should get the title in your name and make sure it’s registered in your name. Also make sure you’ve got your own insurance for the vehicle. If that’s not possible, then you don’t own the vehicle yet, legally speaking. I’d try to settle it with your dad before it comes to that. It’s luck of the draw when you get the police involved, and then they’re in charge. It doesn’t always go the way either side wants it to.