Casey Affleck has admitted buddy Joaquin Phoenix’s erratic behavior — the beard, the retirement from acting, the promised hip-hop career — was a put-on for his now-released mockumentary I’m Still Here. And now an interview with Late Show with David Letterman writer Bill Scheft, published in Indianapolis’ indie paper Nuvo last year, reveals that Dave was in on the joke when he did the notorious crash-and-burn interview with Phoenix last year, during which the actor stuck his gum under the desk, mumbled answers amid awkward silences, and generally lacked any sense of consciousness or humor. “Think Andy Kaufman without shaving,” Scheft said. “That’s what he was doing. And Dave knew about it and Dave loved it because he could play along. He could do whatever he wanted with it. And he did, and it was great television. But I will take credit for the line, ‘I think I owe Farrah Fawcett an apology.’ That line was mine. I gave that to him during the break.”

Watching it back again, you can sorta tell Dave’s got a few too many zinger lines like that at the ready:

Other possibly telltale signs?

* The insane hyperbole with which Dave repeatedly hypes the tiny indie movie Phoenix is ostensibly there to promote, Two Lovers. A way to highlight Phoenix’s great “fall” from rarefied heights of respected actor-dom to crazytown? An attempt to make sure the movie got its due despite the insanity of its star? Not sure, but he laid it on awfully thick before the actor graced the stage (at about the :30 mark here), an odd choice, to be sure: “What a fine piece of work,” he said, then continued: “This was just a lovely, nice, well-acted, interesting story, very insightful, a beautifully done film…It opens on Friday in selected cities. I just pray to God your city has been selected.” I wish they’d used that last bit as a blurb in the ads — it’s classic.

* Is that another of Phoenix’s “nervous tics” when his mouth twitches around 3:05 (in response to Dave’s question, “What can you tell us about your days as the Unabomber?”), or is he stifling a hint of laughter?

* Around 9:10, as they cut to the clip of the movie, Phoenix checks on his gum to make sure it’s sticking underneath the desk, which seems an odd thing to do for a guy who acted impetuously in sticking it there a minute earlier.

* Their whole interaction at the end as it cuts to a commercial — Dave saying “Good job” and shaking his hand, Phoenix taking his sunglasses off to signal the end of performance. Might be the clearest indication of their collaboration.

Though it should be noted, we believed Dave was nothing more than an innocent victim at the time. Congrats, Dave, for holding your own, acting-wise, against a two-time Academy Award nominee who was in the greatest movie of all eternity, Two Lovers.

What do you think when you watch this clip now, PopWatchers? Any other clues you noticed?