At some point, I ran across an argument along the lines of: "We hunger, and food exists. We thirst, and water exists. We feel horny, and sex is real. We yearn for God, and so I conclude that God exists."

Now, I can easily pick this apart a bunch of different ways, the easiest one being that just because you want some to exist doesn't mean that it really exists. But what I'm really hoping for is a couple of counterexamples: something like "Yes, well, we all want a unicorn, too, but unicorns don't exist."

This particular one doesn't work because wanting a unicorn isn't a universal desire the way food or sex are (even counting asexual people, we can still say that the vast majority of people want sex). But maybe some of you can think of something.