I'm going to key my dad's car after he insulted my friend
What is the reason for you wanting to key someone else's car?
He is not my real dad
Keying someone's car is considered vandalism and could lead you to more serious circumstances if you're not careful. You should instead talk to this person and use your words to get to the bottom of their behavior.
I think it will be entertaining to key the car.
While you may find it to be entertaining, you are really doing some serious damage to the car. Nobody deserves to have their car keyed even if they did insult your friend. All that is going to do is make your relationship with your dad even worse.