Last night Joaquin Phoenix returned to David Letterman's show for the first time after his infamous FAKE ASS visit of a year and a half ago. He kind of explains and kind of apologizes:

I think Letterman has a point about being owed some cash. Also, I need a break from "documentaries" that are fake. Though apparently the (impressively large amount of) vomit was real, according to Casey Affleck's tell-all with Roger Ebert.