What are some flat earth style theories you feel like you could debunk, even if you aren't a specific expert in the related fields? What are some arguments in against crackpot theories that have easily explained holes?

I'll start
I don't think we're living in a simulation because it would probably take more energy to recreate the universe that there is in the universe

Wouldn't a perfectly simulated universe require infinite energy so that each universe simulation could simulate a universe inside of it?
Even if simulating 1 electron only required 1 electron to move across 1 IC, that would at most be 1:1 scale