I don't really want my 20-year old son
Why don't you want your 20 year old son?
He makes bad choices in his life and he does stupid stuff.
You should accept your son even if he makes bad choices. You should talk to him and help him because disowning him will push him further into bad decision making.
If he didn't listen to me as a kid, he won't listen now and I am fed up with him anyway.
Walking away from your son because he hasn't learned to make good choices is not a good choice for you and it hurts him. Make time to support him with his decision making process and you will see he can learn when supported by you.