[rodoxcasta]

That, I always have difficulty with these types of replies.

What should you do when someone, in a serious discussion, says that the Earth is flat, with a straight face?

Are they mocking you? Perhaps mocking the debate at hand? Are they trolling? Or maybe they are just naive and don't know that they are embarrassing themselves?

Maybe just treat them as a troll? But the thing is that when they appear just as some naive, maybe young person, the generous take would be to explain the ridiculous thing they are saying.. but I always feel so fool when I do that. Plus, I don't have the patience anymore.