"I think it's behavior he should be working on improving" Why? There are plenty of things that people can work toward improving. He doesn't see his behaviour

"I think it's behavior he should be working on improving" Why? There are plenty of things that people can work toward improving. He doesn't see his behaviour as something that requires improvement. You think rudeness is morally unacceptable. He doesn't. You are free to disagree and never work with him if you so choose. But you can't legitimately claim authority on the better way based solely on personal opinion.