What nonsensical beliefs can an atheist believe in?

Atheism isn't about what a person can or cannot believe in. It's about what a person doesn't believe in, it's a descriptive term, not a prescriptive term. The only thing atheism addresses is not believing any gods exist. A person could conceivably believe just about any nutty thing (you listed several) and as long as none of those necessitated a god or gods of any sort existing, then they would accurately be called an atheist.