In many places, it is legal to decorate your car with Christmas lights. However, there are some restrictions on how you can do this. For example, some states have laws that prohibit using lights that are too bright or that could distract other drivers. In addition, it is important to make sure that the lights are securely attached to your car and that they do not cause any safety hazards. So while it may be legal to decorate your car with Christmas lights, it is important to follow the rules and regulations in your area.