Proof that God doesn't exist

This is from The Hitchhiker's Guide to the Galaxy

Now it is such a bizarrely improbably coincidence that anything so mindbogglingly useful the Babel fish could have evolved by chance that some thinkers have chosen to see it as a final and clinching proof of the non-existence of God.
The argument goes something like this: “I refuse to prove that I exist,” says God, “for proof denies faith, and without faith I am nothing.”
“But,” says Man, “the Babel fish is a dead giveaway isn’t it? It could not have evolved by chance. It proves you exist, and so therefore, by your own arguments, you don’t. QED.”
“Oh dear,” says God, “I hadn’t thought of that,” and promptly vanishes in a puff of logic.