Joaquin Phoenix is not to be trusted. That should be obvious given his history, and yet he’s still duping people. Last night he visited the set of the “Late Show With David Letterman” where he told (and re-enacted) a fantastical story about how he met his yoga instructor fiance.

And this morning he revealed that he doesn’t actually have a yoga instructor fiance.

There were a number of red flags with the narrative. The pair allegedly met when he attended her class and she assisted him in a shady-sounding pose. Even Letterman, who never struck us as much of a yogi, seemed skeptical about the so-called “harnessing of the hog” posture.

Joaquin Phoenix in a scene from the film, “Her.” When he’s not acting, he’s still acting. (AP Photo/Warner Bros. Pictures)

“That’s a carnival ride,” Letterman said. But Phoenix was persistent. He got on the ground to demonstrate the move, narrating the interaction he had with his betrothed:

“So my Julio Iglesias is up next to her goulash and she’s thrusting,” Phoenix explained. (No, we weren’t familiar with those euphemisms either.) Once he made it back to his chair, he delivered the heartfelt kicker: “I think she’s the one. I proposed to her and she said yes.”

The audience was thrilled.

But this morning on “Good Morning America,” he clarified.

Which is to say, he confessed that it was totally made up.

“I think like my life’s so boring, and it seemed like something exciting to talk about, and I wanted the audience to like me,” he told George Stephanopoulos. People like stories about engagements, he noted. He offered to make up another engagement story right there on the spot.

If you’re one of the many viewers (or many news outlets) that was ready to send Phoenix a new toaster and note of congratulation — well, you have a short attention span, don’t you? This isn’t the first time he’s pulled an off-beat stunt. It isn’t even the first time he’s pulled a off-beat stunt on Letterman’s show.

In February, 2009, Phoenix was promoting “Two Lovers” when he turned up on “The Late Show” with an impressive beard, sunglasses, shaggy hair and disturbing lack of social skills. It was difficult to watch, as Letterman attempted to ask questions and Phoenix struggled to emit single-word replies. Letterman probed Phoenix on his supposed retirement from acting and pivot into a rapping career, and the exchange went like this:

Letterman: You’re not going to act anymore?

Phoenix: No.

Letterman: Why is that?

Phoenix: Mmmm. I don’t know.

People either delighted in the trainwreck or showed concern for the actor’s well-being. Dr. Drew Pinsky even attempted to diagnose Phoenix based on his erratic appearance.

“He was dysarthric, a specifically thick tongue that again is difficult if not impossible to mimic. And finally there was severe motor slowing which is a yet another feature of intoxication or a severe psychiatric condition such as depression,” Pinsky said

“Not impossible,” indeed. For an Oscar nominee who once transformed himself into Johnny Cash, mimicking dysarthria or whatever was clearly child’s play. As we all learned soon enough, it was just enough stunt, staged for Phoenix’s documentary “I’m Still Here,” directed by Casey Affleck. The “Borat”-esque movie chronicled our collective culture’s obsession with celebrity and incomplete grasp on reality.

Phoenix elaborated on the movie during his subsequent, much more cordial Letterman appearance, in 2010.

“I started watching a lot of reality shows, and I was amazed that people believe them, that they call them reality. And the only reason why is that it’s billed as being real and the people use their real names, but the acting is terrible,” Phoenix said. The actor also said he was shocked by the way people witnessed his over-the-top antics and never questioned their validity.

And yet, here we are, once again believing everything Phoenix says, even when those things are completely outlandish. When the Hollywood Reporter got a hold of one of Phoenix’s reps, the response was: “How about the fact that he happens to have an extraordinary spontaneous sense of humor?”

Something like that. Let’s hope the stunt doesn’t hurt his chances of finding a goulash soul mate for his Julio Iglesias.