Your very existence is proof of a Creator. Look everywhere. Matter is proof. Light is proof. Life is proof. In fact, even civilization is proof. With all of your intelligence and reasoning, how could you overlook such glaring evidence?
I'm never quite sure how to respond to such a remark, not because it stumps me, but because I would like to think that people are not so naive. I know that Christians believe god created everything, but an atheist obviously does not believe that. Even when I was a believer, I would not have made a pathetic argument as generic and useless as this one. There's nothing about existence, matter, light, life, or civilization that compels us to accept theism. In fact, the latter four are pretty well understood in terms of natural explanations. As for my existence, I take it as proof that an egg containing my genetic material was fertilized and carried to term, but beyond that, nothing more can be reasonably assumed.
For an analogy (and I do love using analogies so very much), this is kind of like a Mac user trying to explain the 'obvious' superiority of Macs to a PC user. The two have different perspectives, which means that it cannot be assumed that one will share the same approach to the issue as the other will. But it's even worse in what this Christian is saying, since he's making an argument based on things which have natural explanations. Supernatural stories are not necessary. It's like a Mac user telling a PC user that Macs are better because they have monitors, keyboards, processors, and hard drives. Both have them! More importantly, there is no logical progression one can follow to conclude that such an argument favors Macs, just as there is no logical progression to demonstrate that earth, wind, and fire (couldn't resist) favor the existence of a deity.
I can't really see why any intelligent person would find this to be persuasive. It seems that the believer's only source here can be the bible, and in that case, the argument is circular. The bible says god created everything, so we can look at everything as evidence that a creator god exists, just like the bible claims. But why the Christian god? The Qur'an claims Allah created everything. The Babylonian epic Enuma Elish claims that Marduk created the world out of Tiamat by dismembering her corpse. Existence, matter, light, life, and civilization no more prove that the creator is Yahweh than they prove that Allah or Marduk is responsible for creating it all. Then there are those things that believers never seem to bring up. Is matter evidence for god when it's assembled in the form of a hydrogen bomb that devastates an entire city? What about those corners of the world where light barely reaches - is god not present there? And Michael Bay? Surely, if anything, he's evidence of an incompetent creator!
A being that can be proven to exist by anything is worth nothing. It's funny, then, that the most common application of the god concept - and the reason for its very origin, I'd say - is to explain what is not understood. We use god to fill in the gaps and then we point to the gaps to find god. Unfortunately, even when something is well understood by science, some believers take their own ignorance as widespread truth and plug god into that gap. In cases like these, it is difficult to know what to say. How do you tell an uninformed person he's wrong when he will accept any trivial thing as confirmation of his faith? Perhaps it's not even worth bothering. As a dead Jewish carpenter is thought to have once said, "do not throw your pearls before swine."