God is tired of man thinking more highly of himself than he ought to, and he's especially upset now that man is messing with DNA and cloning. So he comes down to earth just as there's a Scientist's Convention going on.
After the last speaker speaks, God walks up to the podium and introduces himself - "Hello, I am God. Yes, I am real, and I am sick of you all trying to play Me. I am the Creator and you need to stay out of my business."
One of the scientists stands up and says, "Well, I tell you what, God. Let's go outside, and if I can make a man, you leave us alone. If I can't, we'll stop."
God agrees and they go outside. God spits in the dirt and starts molding a man out of the mud. The scientist also bends down and takes a handful of dirt.
"Wait!" God says, "Get your own dirt!"