Where did you read that? Most atheists I know, and today's prominent atheists like Dawkins and Hitchens, will claim there is no evidence to prove there is a creator, but as far as I know, none of them has ever claimed they can prove the opposite. Proving a negative is impossible. We can't prove there are no invisible unicorns either, but we can say it's extremely unlikely they do exist.
Hitchens was on TV just the other day and said exactly this. When asked, he agreed he could not prove that God does not exist, but turned the question around and asked how likely was it that God, if he did exist, cared who we slept with and what we ate.
I agree that Dawkins is an arrogant SOB, but I believe you misunderstand his claims about the existence of God.
Well, that’s the point in a nutshell isn’t it? Atheists a believe that there is no God and theists believe their is. But somehow ateists also believe that their belief is the only rational one which is, well, irrational.