Which is not to go so far as to say that if you buy into “Joker,” the joke’s on you. (Except in the long run it really is.) If you live to see Joaquin Phoenix go to performing extremes like nobody’s business, this movie really is the apotheosis of that. As Arthur Fleck, the increasingly unglued street clown and wannabe stand-up comic down and out in what looks like 1980s Gotham (although who knows what period detail looks like in fictional cities), Phoenix flails, dances, laughs maniacally, puts things in his mouth that shouldn’t go there, and commits a couple of genuinely ugly and disgusting crimes with ferocious relish.

Much has been made, by Warner, and I guess DC Comics, of the fact that this is meant as a “standalone” film that has no narrative connection to other pictures in the DC Universe, but that’s having your cake and eating it too when you still name your lunatic asylum “Arkham” and your cinematic DC Universe is changing its Batmen every twenty minutes anyway. Maybe what they really mean is that this is the first and last DC movie that’s going to be rated R.

A rating it thoroughly earns. The violence in this movie means to shock, and it does. Fleck’s alienation in the early scenes evokes Travis Bickle’s, but this movie is too chicken-livered to give Fleck Bickle’s racism, although it depicts him mostly getting hassled by people of color in the first third. Fleck is also fixated with a Carson-like talk-show host played by Robert De Niro, reversing the “King of Comedy” player positions. He also likes the black woman down the hall from him, played by Zazie Beetz. The casting is not just meant to give the movie bragging rights on the zeitgeist curve, but to evoke Diahnne Abbott in both “Taxi Driver” and “Comedy.” Fleck’s seemingly successful wooing of the character is a jaw-dropper that had me thinking Beetz ought to fire her agent, but a late-game clarification makes it … well, forgivable is not quite the word, but it will do.

As Gotham begins to burn (the civil unrest starts with a garbage strike), Fleck, who has been taken as a vigilante by much of the city’s 99%, doesn’t quite know what to make of his underground cult stardom. (The city is beset by rioters in clown makeup and clown masks; because this movie is rather suddenly behind the curve in “clowns-are-scary” awareness—only Pennywise gets a special dispensation these days—these sequences look like “The Revolt of the Juggalos” or something equally laughable.) His mom (Frances Conroy, the poor woman) has been writing letters to her former employer, the magnate Thomas Wayne, and Arthur opens one of the missives and reads them, learning something disturbing.