Dump him or keep him?

Been together 9 months and thought things were going smooth until last week. I was having a conversation with my him about my mother and he jokingly called her a retard. I asked him not to do that and he said that he doesn't understand why I would be offended because other people don't seem to mind. So I told him that I find it disrespectful and it rubs me the wrong way. He apologized with a pissy attitude and that really upset me. I asked him why he was getting short with me and he said that my request was disturbing to him. I was trying to be as nice as possible, but his narcissism kept getting in the way. He just can't be told anything and then I got so upset. I don't think I want to date him anymore.