You know a talk-show appearance hasn't gone well when the host ends the segment saying, "I'm sorry you couldn't be here tonight."

That's how things went down on Wednesday night, when a dazed-and-confused-looking [movieperson id="166907"]Joaquin Phoenix[/movieperson] visited "The Late Show With David Letterman," ostensibly to promote what he has said is his final acting gig, "Two Lovers."

Sporting his Grizzly Adams beard, a black suit and dark Miami Beach grandma sunglasses, Phoenix nervously chewed gum during the entire sitdown, often looking down as if asleep. He answered Letterman's queries with one or two befuddled words and acted surprised when the audience and host laughed at his apparent cluelessness.

After praising the actor, Letterman opened the interview by asking him about the beard. "It's been three years since the last time you were on the show, and I will just say right off the top here, you look different than I remember you," Letterman said. "You've got a nice beard going. ... How is that, the beard?"

"In what way?" Phoenix replied.

"Is it comfortable? Is it itchy? Are you pleased with it?" Letterman asked.

Mumbling a bit, Phoenix said, "I'm OK with it, but now you're making me feel weird about it. ... Is there something wrong?"

Letterman, leaning in, quipped, "I can't be the first one to make you feel weird about it."

Phoenix also seemed unsure when Letterman asked him about his co-stars in the movie. Taking a long, lingering sip from his coffee cup after the question, he forced Letterman to remind him that Gwyneth Paltrow plays opposite him in the film.

"You were terrific in it, and I really enjoyed your work," Letterman said, trying to draw Phoenix out.

"Thank you," Phoenix mumbled, inspiring Letterman to do one of his infamous silent, lip-chewing awkward pauses, as the audience roared with laughter at the bizarre exchange and awkward silence as Phoenix looked out in a daze. Letterman appeared charmed at first and seemed to play along, but when Phoenix failed to answer any of his questions, the host went into his Paris Hilton takedown mode, asking Phoenix, "What can you tell us about your days with the Unabomber?"

[article id="1603702"]Phoenix has said he's quitting acting[/article] to focus on his burgeoning hip-hop career. ("Two Lovers" director James Gray told us Phoenix has even built a recording studio in his house.)

But with brother-in-law Casey Affleck following him around to film his every Andy Kaufman-esque move, speculation has been raised that the acclaimed actor is either having a public breakdown, suffering from a substance problem or [article id="1603675"]playing an elaborate prank[/article] on the media for the purposes of the documentary. Letterman asked about his plans to take time off from acting, quipping "and I think you're taking a little time off tonight." He later urged Phoenix, "I'm hopeful that you will reconsider and come back to acting, because there's nobody really better than you are."

Phoenix repeated that he would not be acting again. When asked why, Phoenix said, "I don't know," to which Letterman replied, "So, you've given it some thought."

When Phoenix explained that he would be making a hip-hop album, the audience laughed and the seemingly put-off actor grumbled, "Is that the joke? What do you have them on? What do you gas them up with? Is there nitrous kicking around in this joint?"

The actor said he was working on his debut album and would like to come on the show again and perform at some point. "You know, that seems unlikely," Letterman said.

The final straw came after Letterman asked Phoenix about "Lovers" again, which the actor said he hadn't seen. "What a surprise," Letterman laughed.

Asked to set up the clip of the movie, Phoenix again paused, causing band leader Paul Shaffer to guffaw loudly. "Are you f---ing kidding?" Phoenix said, looking over at Shaffer. "Are you serious? Does the maniacal laughter ... I don't know what the clip is?"

"Maybe a scene with you and Gwyneth Paltrow," Letterman offered, trying to bail him out.

When Phoenix seemed put-off, Letterman said, "We're having fun. Just relax, seriously. I'll come to your house and chew gum."

The unflappable host signed off with what will now be one of his all-time great zingers, "Joaquin, I'm sorry you couldn't be here tonight." The improvised line drew a smile of recognition from Phoenix, which may have indicated that the appearance might just be a joke. "You're funny," he said.