Joaquin Phoenix gets the last laugh after all.

For months, he earned entertainment headlines on a par with Britney or Lindsay or any other misbehaving celebrity. And it was all a hoax.

The movie about it, his brother-in-law Casey Affleck’s documentary and excuse to follow him on the road and attract sexual harassment lawsuits (Can we believe those either?) is titled “I’m Still Here” and is ugly actor personified. But if Phoenix is truly “acting” all these outbursts, tantrums, stoned rambles and embarrassing encounters with the likes of Letterman and Ben Stiller, Edward James Olmos and Mos Def, then it’s the performance of his life.

The film, opening Friday at The Enzian, is framed with a home movie moment, of young Joaquin (Joaquin Rafael Bottom was his name then) summoning up the courage to dive off a waterfall for his free-spirit hippie dad in the jungles of Panama.  Twenty years later, the adult Joaquin summons up the courage to plunge into his “retirement” from films.

“I don’t want to play the character ‘Joaquin’ any more,” he mutters. His speech is so slurred in Affleck’s film that they use subtitles half the time so that we can see what he’s saying. Not that it’s deep or anything. He’s just playing a guy burnt out on the level of fame he’s achieved, ready to check out of that (pharmaceutically, at times) and try his hand at rap.

Nobody took the rap career thing seriously. Nobody. And having him fly back and forth across the country in pursuit of the deadpan super-producer Sean “Formerly Puffy/P.Diddy” Combs doesn’t change that. He can’t sing, can’t keep time with the beat. And growing that Hasidic beard didn’t help.

But what emerges from this year long hiatus, with faux rants at his friends/assistants, meltdowns on stage and bouts of vomiting and nudity, is almost a commentary on our fame-for-fame’s-sake culture. “The character Joaquin” wants to check out, but can’t handle losing the limelight. He wants to do his thing, but his new thing is just ludicrous spectacle. And when the perks of celebrity drift away — he feigns anger at not getting into any Obama inaugural activities — he acts the part of the jilted star on the fade, the whole “I used to BE somebody” bit.

A promising bit, sitting down for a little career counseling with “E-jo,” Edward James Olmos. When you can’t tell if either actor is sincere (Olmos appears to be), there’s no joke.   At least Letterman knew how to get laughs out of the absent-minded appearance where Phoenix was supposed to plug his “final” movie, “Two Lovers.”

It’s all tiresome, muddied and artlessly made. Those camera phone videos of his performances were all the production values this stunt deserved. And if this little game he played — which was just close enough to the real “intense, emotional” highly strung and often rude guy he comes off as in interviews — hurts his “comeback,” so be it.

Maybe he’s just “admitting”  “hoax” as one last effort to save face from a disastrous mockumentary that is only funny when Sean Combs is pretending to be interested in his music. Even as a fake pot-bellied wreck of a pothead, Joaquin or JP or whoever he wants to call himself, is just not funny.

Cast: Joaquin Phoenix, Casey Affleck, Ben Stiller, Sean Combs, Edward James Olmos

Director: Casey Affleck

Running time: 1 hour 48 minutes

Rating: R for sexual material, graphic nudity, pervasive language, some drug use and crude content