I was reading the first volume of Pope Benedict's Jesus of Nazareth today, and he quotes the second century Church father Theophilus of Antioch, in his book Ad Autolycum ("To Autolycus") , "But if you say, 'Show me your God,' I would reply, 'Show me yourself, and I will show you my God.'"
Benedict was highlighting Theophilus' argument that just as there were physical eyes, there are eyes of the soul, and just as physical eyes can be blinded, so can the eyes of the soul, making it difficult or impossible to see God. But it also made me think of the challenge I hear from the scientoids about what they argue is the lack of hard and fast evidence for God. "Show me your God," is the general point, and you are expected to produce scientific evidence for the belief in God.
The next time you are asked to do this by your atheist friend, ask him "Show me your self," or "Show me your mind," or "Show me your consciousness." Atheists use these terms all the time and no one is expected to give scientific evidence for the things they signify--largely because there isn't any.
The point being that there are things for which you don't need scientific evidence to believe.