Damien Chazelle’s “Babylon” is the movie viewing equivalent of being assaulted by a hot mess, perhaps the hottest hot mess you’ve ever met.

Even as it’s shouting at you and unpleasant, even when you’re most aware that “this will never work out,” you’re bowled over, marveling at how “hot” this mess is.

A sordid, seamy fantasia on Hollywood’s “pre-Motion Picture Code” era of unsafe sets, unsafe drugs and unsafe and uninhibited sex, it is over three hours of every unsavory story you’ve ever read about those freewheeling, scandalous years. Names of stars and would-be stars have been changed, but if you know the lurid lore of 1920s “Babylon” you’ll have some idea of who’s who, and who is doing what to whom.

Nicknamed “Babylon” long before Kenneth Anger’s scandal-mongering expose “Hollywood Babylon” was published, the director who gave us “La La Land” sets out to show us the “real” Hollywoodland. He yanks aside the curtain of just how “Gatsby on Steroids” crazy it all was — decadent, drugged up, oversexed, unpoliced and Prohibition Era drunk.

And if you thought the shock-to-the-system that the coming of “talkies” heralded was no scarier and crueler than “Singin’ in the Rain” depicted it, friend are you in for an awakening.

Brad Pitt stars as Jack Conrad, a mustachioed John Gilbert type at the very top, aside from his latest wife (Olivia Wilde) cussing him out and dumping him as he swaggers into the latest 1926 baccanale, the sort of hedonistic no-holds-barred soiree a studio chief (Jeff Garlin as a Weinstein Golden Age type) would throw back then, a boozy/druggy party filled with hot jazz, hot stars and even hotter wannabes.

Jack is jaded, over doing the old costumed epic nonsense so popular with studio execs. He pretentiously talks up “the art,” wishes he could make films more like those coming from Europe, and reverently references architecture as if has mastered that art, too. Which sounds a lot like Brad Pitt.

Margot Robbie is Nellie LaRoy, a would-be EveryStarlet and uninhibited wild child who shows up drunk, wrecks whoever’s roadster she rolls up in, and proceeds to flash it and “work it” in search of her moment of discovery.

“Honey, you either ARE a star, or you ain’t. You don’t ‘become one.'”

Jovan Adepo of “Fences” and “Overlord” is “hot jazz” virtuoso Sidney Palmer, a Louis Armstrong type who faces less racism in Hollywood than perhaps he would in the rest of the country, until that humiliating moment when he figures out these white folks don’t know how to light and photograph Black folks. They want him to cover his face in burnt cork so that he looks like the rest of his band.

And the film’s fourth distinct point of view is of the Mexican immigrant Manny (Diego Calva of Netflix’s Mexican series “Unstoppable”). Manny is just a guy bamboozled into getting an elephant to this party and is perhaps the most iconic Hollywood “type” of all. He’s a fixer. He’s that person on the studio lot or on location who takes an assignment, a whim or a wish by those in charge and by God makes it happen. He gets that elephant to that party, kids. Damn straight he does.

There’s always a place in show business for a can-do hustler like Manny. Jack picks up on Manny’s superpower. Directors, studio chiefs, and everybody in between will be just as impressed as he rises up the food chain. But at that party, Manny bumps into Nellie and is smitten by this hot mess in a way that’s going to last this entire three hour and eight minute epic.

Labeling “Babylon” itself a “hot mess” doesn’t just refer to the stars and starlets misbehaving as if there’s no tomorrow — because as we see, people were killed in on-set accidents, drunkenly driving home from parties, overdosing on drugs and alcohol or sexually assaulted by the perverts prowling such parties. Careers ended in a lot of ways, and the end was too often terminal when the dreams were this big and the fall could be that steep.

Chazelle accentuates the ugliness, opening the film with projectile pachyderm pooping and as many shots of bombshell du jour Margot Robbie vomiting as her contract allows. It’s a movie that positively reeks of sweat and sex and vomit and desperation.

As the thunderous jazz score by “La la Land” composer Justin Hurwitz pins you to your seat in that cacophonous, roiling opening act, it really does feel as if Chazelle is assaulting both the senses and the sensibilities of anybody willing to be plunged into this inferno.

We go to the set of a Medieval epic, and note that out there, in a Los Angeles with less development and more wide open spaces, multiple scenes and multiple pictures are being shot in the same valley, at the same time. Actors stagger in straight from that party and are greeted with a different sort of shouting, extras-wrangling bedlam.

One can’t help but wonder if that experience wasn’t shared by the players in this film about making films, finding your way through managed mayhem. Pitt is grand as the sage veteran of the work and the scene. Robbie is carnal chaos incarnate, and the only way she and Nellie can get through this is by crowd surfing the riot Chazelle is staging and filming.

For me, the first sign of genius is when the second act begins. The overnight revolution that “The Jazz Singer” forced on Hollywood — “talking” and singing pictures — turns riotous, rowdy moviemakers into frazzled “QUIET on the SET!” Nazis. All are enslaved by this new god, the microphone. “Babylon” turns chillingly quiet.

In one brilliant and agonizing sequence, the now-established B-movie star Nellie must endure take after take of an inane under-scripted scene with no comic payoff, struggling to bring some life via some “acting,” but forced to hit her mark and say her line in the precise spot underneath the heavy microphone, no matter what.

A camera operator, condemned to run the noisy contraption inside of a suffocating soundproof booth, gasps in protest. An assistant director blows his top and Nellie loses it as well as one and all worry if this new way of doing things won’t just take the freedom and “fun” out of their work. It could put anybody who can’t adapt out of a well-paying, ego-and-vice-feeding job.

There’s just so much to take in that even the gossip columnist (Jean Smart, venomous and costumed like silent cinema era Gloria Swanson) has trouble keeping up.

Red Hot Chili Peppers icon Flea plays a mobsterish studio “fixer.” Lukas Haas is a wealthy Angelino producer pal of Jack’s given to falling for every starlet who crosses his path and Tobey Maguire is the kind of mobster who gets rich in such dens of iniquity, supplying every vice — drugs, sex and gambling credit.

Famous names like William Randolph Hearst, his paramour actress Marion Davies and MGM wunderkind Irving Thalberg (Max Minghella) flit in and out. Li Lun Li is Lady Fay Zhu, an R-rated chanteuse and silent film titles-writer who happens to be stunning. She is Chinese-American and a lesbian, a woman with all sorts of barriers to making a name for herself once sound comes in and the production code changed employment conditions via contracts with “morality” clauses.

“Babylon” wears out its welcome before it brings these stories to their logical and/or grim conclusions. But for a film fanatic, it grows more fascinating the further we get away from that soundtrack-on-stun/eyes-scorching opening act.

It compares to Tarantino’s “Once Upon a Time…in Hollywood” in glorious ways, and excessive, crude and coarse ones.

For all its fictionalized 1926-34 “history,” the Hollywood period Chazelle really summons up here is the late’40s and early 1950s, when desperate film studios were first confronted with the cathode ray tube TVs flooding America.

“Make it BIGGER” became the mantra. “Make it LOUDER. And in STEREO.”

“Babylon” is gorgeous and grotesque, huge, noisy, and unlike anything else we’ve seen or heard on screen this year. Like “Avatar: The Way of Water,” this isn’t just a movie, it’s an event. And big screen events, even the hot messes, aren’t meant to be watched on Netflix on your iPhone.

Rating: R for strong and crude sexual content, graphic nudity, bloody violence, drug use, and pervasive language.

Cast: Brad Pitt, Margot Robbie, Diego Calva, Jean Smart, Jovan Adepo, Li Jun Li, Jeff Garlin, Flea, Olivia Wilde, Lukas Haas and Tobey Maguire

Credits: Scripted and directed by Damien Chazelle. A Paramount release.

Running time: 3″08