Argumentum ad Lapidem?
The appeal to the stone
According to Wikipedia, the argumentum ad lapidem, or appeal to the stone, "consists in dismissing a statement as absurd without giving a proof of its absurdity."
This supposed fallacy takes its name from the following incident reported in Boswell's Life of Samuel Johnson:
57. Refutation of Bishop Berkeley
After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it -- "I refute it thus."
But where is the fallacy? If the good bishop really did maintain the nonexistence of material objects such as stones, then Johnson really did refute him by drawing Boswell's attention to a massive stone and the resistance it offered to Johnson's foot. But of course Berkeley was not an eliminativist about material objects. He did not maintain that rocks and trees do not exist; he did not deny or even question whether they are; he offered an unusual ontological account of what they are, namely, ideas in minds, including the divine mind. If you know your Berkeley you know that what I just wrote is true and that the bishop cannot be refuted by kicking a stone.
Johnson's mistake, therefore, was not that he simply dismissed Berkeley's thesis without argument; his mistake was that he took Berkeley to be maintaining something other than what he in fact maintained, and then went on, stupidly, to refute this other proposition.
Johnson's fallacy was the ignoratio elenchi, not the ad lapidem.
There is something fallacious in the very notion of the ad lapidem fallacy. I rather doubt that we have any need to add this so-called fallacy to the grab-bag list of informal fallacies. Surely it cannot be the case that it is always wrong to dismiss a statement as false or even absurd without proof. Some claims are refutable by kicking. Suppose you are an eliminativist about sensory qualia; you maintain, for example, that there are no pains. Without saying anything, I kick you in the shins with steel-tipped boots, or perhaps I kick you higher up. I will have brought home to you the plain falsehood of your claim. The fallacy behind ad lapidem is the notion that no assertion can be legitimately dismissed, that every assertion, no matter what, must be paid the respect of an explicit discursive rebuttal.
Or suppose sophomore Sam says that there is no truth. I would be fully within my epistemic rights to respond, 'Is that so?' and then walk away.
Some claims are beneath refutation.