I know Joaquin Phoenix has said he’s quitting acting. Well, he just put in a career-ending performance tonight on David Letterman. (That’s Joaquin below, looking like he just joined ZZ Top…) The guy is way too talented to be behaving like this when he’s supposed to be promoting his latest movie Two Lovers. Or else the joke’s on us — and he’s just goofing for Casey Affleck’s mockumentary on him and his supposed foray into the music biz. I’ve learned that Casey was indeed backstage at the show. But Dave and the rest of the staff truly thought this was for real. Was it?