Girl, if I were you, i would stand my ground. It's your hair, he can't threaten you with you not getting your permit. Over Thanksgiving, my mother wanted me to straighten my hair and i fought with her. I won, of course (it sounded better in my head) and i did my hair natural. All i can say is give him the reasons why. You worked hard to keep it this way, and flat ironing it is bad for your hair. tell him about heat damage and how its irreversible. And if you're uncomfortable with it straight, you should tell him. You should be comfy on a holiday like Christmas. If your dad has a problem with it, it's his problem, not yours.