I have a colleague who is really quite competent in the matter itself, but has really horrible people skills. He is quite full of himself, *everything* is a competition to him and has even received feedback for being arrogant from the customer. So to a certain degree it is known that he is maybe not the best choice for anything management or official commucation related. However I have heard that he is about to be promoted to a senior role which involves exact those points. I am a bit concerned about this, also as I have to closely work with him. I know that this should theoretically not be my business but the impact on the daily business and the team is just to big to ignore it.
How do I tell my boss (we don't have HR) about my concerns regarding this without actually talking bad about this colleague?