I'd actually soften the criterion, myself. Instead of proof, I'll settle for evidence. That's all; basic evidence, that substantiates the existence of whatever pet god in in question and which can only be evidence for that god and nothing else. So far, the cupboard is bare.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'