There are some people who were brought up eating cetain foods and want try something new. if this is his case, there is not much you are going to do to change his mind except let him eat what is served or cook for himself.I have several people in my family that are meat and potato people. They will eat a salad if it only has their favorite vegetable in it They are healthy and don't seem to be lacking in anything, maybe this is what the body is use to after years of eating the things they like. If it's not killing them, let them be happy I guess. It's better than having a heated discussion.