Whatever the assigned definition is. If, for example, you stated that 'god' was an entity that lived under and was visible under every buttercup I would argue non-existence on the basis that I had looked under buttercups and found no such thing, (dependant upon further definition - i.e a blue, six armed, elephant headed dude).
If you want to impress me give me your definition and we can work from there.
Nope, this is an experiment in atheism, not a debate on my concept of God.
So basically although you have no concept of God, you argue against their concept because er, you cannot find agreement with it.