Indeed, Joe has hit the nail (that really does exist) on its head (which does have a result, in reality). Ask your atheist friend to define murder. It will require the use of a word like "unjustified" or "wrongful" or something like that. Then, your atheist friend (just like getting punched in the face) will have zero capacity to justify his belief that there is such a thing as "wrong" or "right" or "murder". When your atheist friend places moral expectations upon you, your atheist friend is stealing from the Christian worldview. He cannot justify his haughty, holier-than-thou request. Remember, the existence of God is proven by the impossibility of the opposite.
The existence of God is proven by the impossibility of the opposite. GB