A number of bad analogies between Santa Claus and God could and have been used. Some of them are so bad they are enjoyed only by atheists bad at philosophy and by bad Santas.
One reason this is a bad analogy is that we can indeed provide evidence against Santa’s existence. Indeed, one of my pet peeves about Christmas movies where Santa Claus is real is that the parents don’t realize it. Consider the following conversation:
Dad: I’m sorry son, but Santa isn’t real.The fact that this sort of thing doesn’t happen is pretty good evidence against Santa’s existence.
Son: Then who got me that bike for Christmas?
Dad: We did, your mother and I.
Son: Which one of you actually put it under the three?
Dad: Your mother.
Mom: I didn’t put it under the tree, I thought you did.
Son: And who got me that toy train track for Christmas last year?
Dad: I didn’t.
Mom: Neither did I.
Dad and Mom: HOLY FECES!
A better but less interesting analogy is that just as we have no evidence for Santa, we also have no evidence for God. At that point one can just put forth evidence for God, like morality (via the moral argument; see also Bayes’ theorem and the moral argument for a simple mathematical look at the evidence) and the existence of the universe (via the Leibnizian cosmological argument; see also my entry on Bayes’ theorem and the LCA). At any rate, analogies are no substitute for real evidence and substantive arguments for atheism.