Well... considering the gods are quite literally the universe, reality, everything, and then some? Not believing in any of those things would be a very serious mental health problem. I've yet to meet anyone who actually has this mental health problem, though; I've yet to meet anyone who doesn't believe in the gods (aka, the universe, reality, everything, and then some). It's why I don't believe in atheists. I believe in humans who don't grant the title "god" for things that they utterly depend upon for having functioning lives (or lives at all) for some reason, and those people can be "atheists" or "theists." By extension, refusal to believe in anything that is greater than oneself or that one depends upon for existing sure does cultivate an extreme level of hubris and narcissism. That's also (usually) lacking in people who call themselves "atheists" or "theists."
Did I mention how useless the terms "atheist" and "theist" are? I'm mentioning it now.