From the street-art shenanigans of "Exit Through the Gift Shop" to the Facebook fraud of "Catfish," some of the year's most popular documentaries have one thing in common: their veracity called into question.

People wondered the same about "I'm Still Here" while it was being shot. Here, after all, was actor Casey Affleck ("The Killer Inside Me") chasing his twice-Oscar-nominated brother-in-law, Joaquin Phoenix, around, documenting the "Walk the Line" star's apparent descent into madness.

He's given up acting! And maybe even hygiene! He wants to record a hip-hop album! He's doing drugs! And, hey, did you see him on David Letterman? What up with that?

Affleck and Phoenix denied it all along, but once their so-called documentary was complete and shopped to distributors, the pair had to admit that, yes, indeed, the whole thing was a joke.

So why isn't it funnier?

"I'm Still Here" screens Friday and Saturday night at Oklahoma City Museum of Art. It's evident from the start that Phoenix's lost two years were staged. For one, his opening rant sounds too much like an establishing setup. For another, when a dear family member's in trouble, you don't grab a camera and encourage bad behavior; you get them help.

The guys could've used some in making their story more solid in its first half; instead, it's as loose as half-formed Jell-O. Whether or not "Gift Shop" and "Catfish" are 100 percent real life, at least they each tell an utterly compelling tale.

For a while, "I'm Still Here" is little but Phoenix mumbling and talking like a madman, chain-smoking all the while. We see him partying with prostitutes, snorting coke off one's nipple before retreating to the mattress.

He talks incessantly about wanting to be "an artist," presumably choosing rap as an outlet because, well, he's white; ergo, insta-laughs, right? Of course he's not any good at it, even when speaking to his assistants in rhyme. (And about those assistants: For fun, Phoenix often has them pull out their genitals, and they happily comply.)

About halfway through, "I'm Still Here" gets its act together by milking this would-be musical career for all it's worth. In the best scene, that would be a lot, as Phoenix, hoping to score Sean Combs as a producer, plays disastrous demo track after disastrous demo track to the befuddled Diddy. It's so uncomfortable and awkward, and yet hilarious, that one wishes all of "Here" adhered to this "Borat"-esque template.

But it doesn't, and the helium they blow into this balloon all but seeps out before reaching the anticlimactic end. As performance art, the movie definitely succeeds in making Phoenix an insufferable ass.

And at what cost? I hope the bros-in-law had a helluva time, because I'm not certain the rather gifted Phoenix can recover from the negative stench that sticks to him long after the closing credits.

My takeaway: There is a stellar director in the Affleck family. His name, however, is Ben. —”Rod Lott