Let me preface this with saying that I do not mean any of what I say here in an argumentative tone, so please read as if it is conversational opinion and questions.
Having an outward symbol of your faith where other's can see it is not the same as pushing your religion on others. If he were to be saying "I won't talk to anyone who doesn't display a cross at their workstation" or " I can't speak with you about anything outside of work because you are not of my religion, a la witness mentality, then that would obviously be different, but from what you described, it seems like he is just decorating his personal space with objects that have meaning to him and going about his business.
Could you be reading into the situation and applying a superiority complex to him that is undeserved? I certainly know that there are christians with a superiority complex out there, but not every christian thinks they are better than others.
It almost seems like having faith (if you are a christian) is on it's way to being viewed as some kind of crime, a case where it has to be hidden in some dark, back room- as of publicly admitting to Christianity is an affront to those who are not a christian, rather than a simple right of personal expression.