I'm not sure anyone would deny that Joaquin Phoenix has always been a little crazy. I could be wrong about this, but I'm almost positive that his whole "there's frogs on my head" red carpet walk was during press for Walk the Line, which happened at least a year before the documentary started. But the type of crazy he displays in I'm Still Here is just sort of sad. To believe that this is real, you essentially have the believe that his friends and management team are all terrible people. How else could they not only watch their friend and client self-destruct like this (doing lots of cocaine, having both private and public meltdowns) without intervening, but in some cases, actively encourage him, and record it all? It may not be completely unfathomable, but still, it's hard to believe.
But assuming you believe/know that it was a hoax, that still leaves two questions. First, who was in on it? Casey Affleck claims that Letterman didn't know about the hoax during Joaquin's infamous interview, but other sources claim that Letterman did know. And what about P. Diddy (since apparently the correct name to call him is "Diddy"...) and Ben Stiller, both of whom make appearances? Diddy seemed guilty, but not too guilty, when he nearly makes Joaquin cry, and if Ben Stiller didn't know the insanity was a hoax, it his Oscar sketch just seems cruel, since he would be making fun of someone who seems to have a real problem. Plus, to be honest, Ben Stiller doesn't seem like he has much of a sense of humor in real life, so I doubt he would agree to have his scenes in the movie if he didn't know. And what about the audience member Joaquin fights at his show in Miami? I'm pretty sure he was planted there for the sake of the movie. I really can't decide whether or not Letterman knew, but I assume Diddy and Ben Stiller did, which seems to simultaneously add depth to the hoax (that so many people knew) and cheapen it (that so many people knew).
Secondly, what's the point? I know this question is asked a lot about art in general, and performance art in particular*, but it really struck me with this movie, particularly as it's described as a "hoax." To me, a hoax seems to have some sort of point, unlike a mere prank. And this doesn't really seem to have a point. Maybe it's to somehow do an expose of our celebrity culture, and how we'll talk about anything to do with anyone famous, and love to hate celebrities to the point of making fun of someone who seems to have a problem. But that point is murky at best. It seems like Joaquin was just always a bit wary of celebrity status, and wanted to see what he could get away with, and what people would believe. And that's not much of a purpose.
Supposedly Joaquin is getting a lot of offers for acting roles after this, which actually surprises me a little. I wouldn't have been shocked if his announcement about retiring from acting was the only true thing in the movie, but I guess not even that is. In some ways it's a complete testament to his acting skills that people were so unable to tell whether this whole thing was real or not. He really does give the performance of his career, as Casey Affleck called it. But just the fact that he did this makes him seem like somewhat of an unlikeable person. Maybe that's just because I'm one of the mass media-consuming people he tried to pull the hoax on. It just doesn't really seem like a springboard to another Oscar-nominated role. But what do I know? At least he'll always have his rap career...**
* I most often think about this in relation to Lady Gaga. Is she Lady Gaga all the time? Is it a performance? Is she in on the fact that its' ridiculous? Does the performance aspect of it undermine the fact that she's talented, or does her talent allow her to do such crazy things? Do I really care, as long as Just Dance and Paparazi are played?
** Turns out he's not quite as bad a rapper as the online videos made him seen. Sure, he's not great, or even particularly good, but he's far from the worst rapper I've heard. In fact, given the love of AutoTune in today's music world, Joaquin could probably have a reasonably successful career, as long as no one knew it was him...