What are some reasons why your mate, or significant other might pick a fight with you? How would you diffuse an argument to keep peace?

We don’t fight. He seems to feel a need to prove that he isn’t vulnerable and doesn’t care about anyone’s feelings. Proudly proclaims himself a prick. I just find something to do elsewhere. He says he doesn’t want a divorce, but also says if I don’t like his behavior I know where the door is, so I don’t really think anything else needs to be said. I feel terribly sorry for him.