I would just tell him that he's never going to convince you of his religion just the same as you are never going to convince him that his religion is false. Then tell him you have to agree to disagree and keep it all to yourselves. If he comes back and proseltyzes some more, kick him in the nuts, and say that there's a swift kick coming every time he mentions god.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell
