This is a subject that I've been fascinated with for a while now; was just discussing it over on Discord. What IS comedy/humor, in fact? How would you explain it to an extraterrestrial? Such a basic thing, seemingly-- probably the most popular, and in many ways safest, of genres... yet also utterly mysterious. (And I'd argue that our quintessential response, laughter, is just as odd. Other animals-- as indicated by the standard online phrase "made me laugh so hard I scared the dog/cat"-- certainly seem to think so.)

Here's my best shot at defining humor: it's a subversion of expectations, where any potential threat (as from surprise) is diffused at the last minute. So we're caught off-balance, then reassured. We thought that we knew where it was going, but we were deliberately misled... and that's OK. Often, the "OK" comes from a sense of general non-seriousness (even if the subject is inherently serious); this promotes a feeling of control, that WE are in a position to ridicule this thing, and derive pleasure from it thereby.

Maybe THAT'S what's meant by someone/something being the "butt of the joke"? That sense of power, control? Though I'd say it's not so much over a person, or even a thing, as... reality. Life. Existence. We manipulate it with humor; we impose our POV on it... we laugh at it.

So when humor fails, I posit that it's a matter of either the subversion or the diffusion failing (or both). In the first case, the audience doesn't share the comedian's expectation, so subverting it leads to "... I don't get it." In the second case, the threat isn't diffused, which leads to, "hey-- THAT'S not funny, asshole!!!"

Andy Kaufman's (rather philosophical) approach illustrates these points: he subverted the expectations of comedy ITSELF, and (for good measure) only diffused the threat in the sense that nothing serious was actually threatened (besides the audience's complacency). It's one of the most original takes on comedy that I've ever heard of, even all these years later.