Here are some suggestions to help you deal with this situation:

1. Direct communication: Talk frankly with your roommates about your feelings and let them know that you don't mind them using your car occasionally, but you also need some private space and time. You can suggest some special days or times, such as when you need a car, or when you need to arrange things yourself.

2. Charge: If your roommate still can't understand your position and continues to rub your car, you can consider charging them a certain car fee. This can help them better understand the cost and inconvenience of using your vehicle.

3. Find alternatives: If your roommate still can't understand your position and continues to rub your car, you can consider providing them with an alternative mode of transportation, such as public transportation, cycling or carpooling.

4. Stay calm: No matter which method you choose, you should remain calm and respectful. Have a frank talk with your roommate and try to find a mutually acceptable solution.

Finally, no matter which way you choose, you should remember to maintain good communication and interpersonal relationships. A vehicle is a convenient means of transportation, but it is not the whole of life. More importantly, mutual respect and understanding.