"Metatheism" is an interesting suggestion. I could not find What is God? by John F. Haught at either the UT or Austin Public Library. However, I did find God and the New Atheism A Critical Response to Dawkins, Harris, and Hitchens by John F. Haught (Westminster John Knox Press: 2008), among several others such as God after Darwin : a theology of evolution. 

I agree with Ed Hudgins above that the best engagement is just to ask the other person what they mean.  I don't know how successful you will be demanding genera and differentia from most of them. That would have to be a separate chat - and most people would suspect that you were pulling a fast one, playing semantic word games. "God created the universe" is just as workable as "God is the being who created the universe." Besides, aside from grammatical niceties such as "being" or "entity" to what genus could God actually belong? God is sui generis.

My wife and daughter bought me a telescope for my birthday, and the skies have finally been clear enough the last month for me to get out whenever I want. Since last November, the one book that I checked out from the library several times is Turn Left at Orion by Guy Consolmagno. (Reviewed on my blog here.) Consolmagno earned a BA and MA in astronomy at MIT before completing a doctorate at the University of Arizona's Lunar and Planetary Laboratory. Some years later, he became a Jesuit brother and was appointed a Vatican astronomer. Consolmagno says that to call God the "creator of the universe" is to reduce Him to a primitive nature deity, like the god of thunder or the goddess of grain.

The New Advent Catholic Encyclopedia says this (among much, much else, on this on several related topics about God) in "The Nature and Attributes of God":

(ii) Yet sometimes men are led by a natural tendency to think and speak of God as if He were a magnified creature — more especially a magnified man — and this is known as anthropomorphism. Thus God is said to see or hear, as if He had physical organs, or to be angry or sorry, as if subject to human passions: and this perfectly legitimate and more or less unavoidable use of metaphor is often quite unfairly alleged to prove that the strictly Infinite is unthinkable and unknowable, and that it is really a finite anthropomorphic God that men worship. But whatever truth there may be in this charge as applied to Polytheistic religions, or even to the Theistic beliefs of rude and uncultured minds, it is untrue and unjust when directed against philosophical Theism. The same reasons that justify and recommend the use of metaphorical language in other connections justify and recommended it here, but no Theist of average intelligence ever thinks of understanding literally the metaphors he applies, or hears applied by others, to God, any more than he means to speak literally when he calls a brave man a lion, or a cunning one a fox.