"Thanks for not being here."

That's what Letterman said to Joaquin during his recent appearance on the the Late Show. That train wreck of an appearance had everyone wondering: Is Joaquin pulling a prank or has he gone batshit insane? My bets are hedged with the former. (Apparently he and friend Casey Affleck are in the process of filming a mockumentary about a hip/hop singer quasi-celeb. So, this may be art imitating life.) That's why it's a little early for reports like these:

A rep for Joaquin Phoenix is slamming a Chicago-based psychiatrist for suggesting that the actor-turned-rapper, 34, is mentally ill. Paul Dobransky — a relationships expert and author of The Secret Psychology of How We Fall in Love — told the Los Angeles Times that Phoenix may be schizophrenic, pointing to his "socially inappropriate behavior," including a new rap career, bushy beard and a bizarre Late Show appearance. But Phoenix's rep tells MTV News: "How absolutely inappropriate for a doctor who has no personal interaction or relationship with someone to diagnose them.""And to do so in a public forum," the rep adds. "Hope they spelled his name right. Another 15-minute 'expert' is born!" [us weekly]