I have to justify that that's what I mean when I say "god," or I have to justify that God created the universe? It is a common definition, so I figured you'd accept it.

The point is I'm not talking about a specific God or assuming anything about the nature of God like many religions do. Once you remove all that baggage God is just a term that means "the thing that created the universe." So to deny the existence of God you must deny that the universe was created by something. I don't see how you can make such a claim without any evidence. Last I checked there was no scientific explanation for the creation of the universe.