My favorite argument.
"You cant disprove god, therefore he exists."
If someone say this stupidity. Say to "him/her" that many scientists think that the "universe" still existed. Also you must precise that this arguments isn't in the right debate because he/she confounded the debate about the "God's Existence" and "Creationism VS Evolution theory".
I prefer claiming to be a god. The obvious reply is "No you're not". At that point, I can simply say "Prove it".