Term for an argument which cannot be distinguished from sarcasm/jest

Alright, I figured it out by searching for "believable facetious argument." I was a little bit off on my definition of it, and it's more of an internet adage than a part of actual English usage. Poe's law is what I was thinking of.

From Wikipedia:

Poe's law is an Internet adage which states that, without a clear indicator of the author's intent, parodies of extreme views will, to some readers, be indistinguishable from sincere expressions of the parodied views.

Thanks for the help though, and upvotes for the effort. :)

When a speaker employs verbal irony, but there are no detectable indications as to whether or not they actually mean what they say, we might call that speaker "straight-faced" or "deadpan".

"Straight face" is defined by Merriam-Webster as "a face that shows no emotion and especially no amusement".

"Deadpan" is defined by Merriam-Webster as "showing no feeling or emotion".

"double entendre"

• double entendre - (noun) ambiguity of meaning arising from language that lends itself to more than one interpretation - synonyms: ambiguity, double meaning, innuendo, play on.

e.g. "The song's title is a double entendre."

EDIT: After reading your comment explaining exactly what you're looking for, I suggest "a facetious statement" or "a misleading statement."

• facetious - (adj) Treating serious issues with deliberately inappropriate humor.

• misleading - (adj) giving the wrong idea or impression

I might offer two possibilities here, both legal terms: from Burton's Legal Thesaurus, 4E. Copyright © 2007 by William C. Burton. Used with permission of The McGraw-Hill Companies, Inc.

SUGGESTIO FALSI. A statement of a falsehood. This amounts to a fraud whenever the party making it was bound to disclose the truth.

SUPPRESSIO VERI. Concealment of truth. 2. In general a suppression of the truth, when a party is bound to disclose it, vitiates a contract. In the contract of insurance a knowledge of the facts is required to enable the underwriter to calculate the chances and form a due estimate of the risk; and, in this contract perhaps more than any other, the parties are required to represent every thing with fairness. 3. Suppressio veri as well as suggestio falsi is a ground to rescind an agreement, or at least not to carry it into execution.