Monkey See Monkey Do
I had a kid who was heading down this road and I have two closely related pieces of advice:
1. Kids learn from what you do, not what you say. So if you have a kid who is an asshole.... you get the picture.
2. “No” has to mean “no.” If “no” only means “no” until your kids screams and throws a big enough tantrum for long enough, you can only assure that your kid will throw ever bigger and longer tantrms (i.e. become more of an asshole).
I had to face the fact with my own son that he was learning from my example of my relationship with his mom. The divorce was ugly. Two decades later his mother and I don’t speak at all and haven’t for many years. However, our son has turned into a fine young man. So there is definitely hope for you and your little asshole.