Casey Affleck has been following Joanquin Phoenix filming him.  Casey was filming during the Letterman show.  At the end of the segment Joanquin stands up and turns his back to audience takes off his glasses and shakes Letterman's hand and says "good job".

Casey and Joanquin are reportly filming a mocumentary.

Sorry but people whom are seeing this as Joanquin having a melt down are being taken for a ride.  It's all a put on.

Read this People article:
http://www.people.com/people/article/0,,20255458,00.html