After he gets a new job, just tell him

that he is nobody. If he believe he is that good as he hopes, why he is not the boss? It sounds very tough to him, but he has to grow up. That is what I tell myself when I got my job, just to remind myself to be careful on everything. It sounds to me he is very spoiled by his family (maybe even by you), and think that he is #1 in the world (I may be wrong). Feel sorry for your experience, but that personality is very annoying to most people. He has to grow up, and hopefully this is a good chance for him to learn things. Sorry for being very straigh.