In 2008, Joaquin Phoenix shocked the world by announcing that he was going to retire from acting to pursue a career in hip-hop. Growing a beard that would put Howard Hughes to shame, Phoenix vanished for a spell before making a bizarre visit to the David Letterman show, where he seemed beset by madness, drifting, unfocused. The world wondered: What happened to this talented young man? And perhaps even more intriguing: Was this all a hoax?

Don't think for a moment you'll find the answer in the tedious documentary "I'm Still Here." Since Phoenix spends half the film with his head down, mumbling and shirtless, "I'm Still Here" is literally (and figuratively) an exercise in navel-gazing.

Casey Affleck was on hand to film Phoenix (also his brother-in-law) from the moment the latter called it quits. We get a firsthand account of Phoenix as he begins to lose his marbles: dabbling in music, hiring prostitutes, snorting cocaine, drinking, shouting at his friends (who, inexplicably, are quite often nude), and, worst of all talking, talking, talking ... about absolutely nothing at all. Are we supposed to applaud Affleck for capturing the banality of a celebrity's life?

Perhaps the only compelling moments involve Phoenix's desperate attempts to get music producer Sean Combs in the studio to listen to his raps. But when they finally meet, the scene is so obviously false that it kills any dramatic impact.

The question of veracity colors every scene, including the infamous Letterman appearance, leaving you feeling taken and, ultimately, bored by the possible hoax.

Late in the film, one of Phoenix's sycophants becomes so angry that he literally defecates on the star's head. It is an apt scene -- whether intentional or not, it sums up exactly what Joaquin Phoenix has done to his audience.