I once had an elder coworker who said all the dinosaurs died in Noah's great flood. I'd try reasoning with him but ultimately it was way more fun to ask him if god could create a rock that he couldn't lift.
I think with people so entrenched in a silly opinion its way more fun to identify their most absurd belief and mock them relentlessly for it. I think for flat earthers its "so where does the air and water go when it falls off?"
