Appeal to the stone

Appeal to the stone is an informal fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity.

Speaker A: Infectious diseases are caused by microbes.
Speaker B: What a ridiculous idea!
Speaker A: How so?
Speaker B: It's obviously ridiculous.

Speaker B gives no evidence or reasoning, and when pressed, claims that Speaker A's statement is inherently absurd, thus applying the fallacy.

Comment fallacy in appeal to the stone on Reddit to explain this fallacy. ?