Look before you leap.
“Off the wall” can be said of anything that does not conform to expectations. It's not restricted to paintings. The irony the once-popular idiom had is long gone and it faces linguistic extinction. It became over-used to caption reviews of art exhibits that defied easy definition. But before it died it redeemed itself by killing-off the previous dumb idiom: “Now I've seen everything."
Rauschenberg revived Dada hilarity-in-art with his Combine “paintings.” Dada on steroids. Although they were classified as paintings, the mere fact they had paint on the list of materials didn't make them paintings. We've come that far since it was arguable whether a painting was, in fact, a painting. Remember "That's not art"? Another art witticism that died on the vine.
It's art if an artist says it's art. Period. Or, as we now say, "full stop." A touch of circular logic to stymie pedants and intellectuals. It was Matisse who said, “A good painting is like an easy chair." It was a profound comment in his day. It was taken literally by artists desperate for inspiration long after art had gone off the rails. We discovered that by smearing paint on any random item of bric-a-brac it could be made into art.
Another artist (now forgotten) thought he was being witty when he took Matisse literally, saying, “And yet, art is not to sit upon.” Or, it might have been the security guard at the Museum of Modern Art who said it. Memory fails.
It is the problem of “repose” in art. The middle term of Matisse's bon mot is that, if an artist seated in his easy chair is made uneasy looking at his work of art, he shall rise from his chair to make whatever adjustments to his work it demands. He will "bestir" himself, that being the antonym of repose.
Until the artist stops work (full stop) the work of art remains unfinished. This is an axiom of productive work in general, adapted to the creation of a work of art. I would add that the privilege of making changes belongs to the artist -so long as he retains ownership of it. Once a collector takes delivery of a work of art he may forbid the artist to get anywhere near it.
It is therefore in every artist's best interest to be certain of the finished state of his work before exposing it to public scrutiny. The exhibitor, an art gallery, for instance, may not wish to have a piece withdrawn by an artist because the artist has had a change of heart. The gallery has an obligation to its patrons. And, where collectors are concerned, not much can be done about an artist's failure to deliver promised work except, perhaps, file in court.
An artist is under immense pressure to decide. Provenance is a historical matter. When a work of art leaves the artist's studio the cat is out of the bag. Matisse's charming quip belies the angst famously attached to Modern Art. He may have had his famous associates in mind, and issued his famous dictum as a provocation, a “head fake,” to jolt them out of the Modernist delirium. Think before you drop.