The two-time Oscar nominee, who recently announced he is giving up acting to pursue a career in rap music, appeared on "Letterman" to discuss what Phoenix claims will be his final movie, "Two Lovers."
Letterman gamely tried to chat Phoenix up, but the "Gladiator" and "Signs" actor barely looked at him and mumbled curt answers to Letterman's questions.
Letterman told Phoenix he liked "Two Lovers" and Phoenix's performance in it, and also said he was impressed by the musical chops Phoenix showed in his Johnny Cash bio-picture "Walk the Line," but the compliments drew little reaction from the actor.
The veteran talk-show host then started teasing Phoenix about his beard, asking, "What can you tell us about your days with the Unabomber?"
Letterman also commented on the fact Phoenix was chewing gum during the interview, which prompted the actor to take it out of his mouth and stick it to Letterman's desk.
Phoenix did, however, tell Letterman, "I'd love to be on the show and perform," to which Letterman replied, "You know, that seems unlikely." Letterman later quipped that he would keep Phoenix's number in his Rollodex just in case.
At the end of the segment, Letterman told the film star, "Joaquin, I'm sorry you couldn't be here tonight."