This is purportedly Michael Cera (formerly of Arrested Development) and director Judd Apatow getting into a fight on set, where Cera was originally cast in the role but was fired and replaced by Seth Rogan.
This is where it gets interesting.
Michael Cera is starring in the next Apatow-helmed movie Superbad later this summer. And remember that Judd Apatow has a wicked sense of humor.
This is a bit of viral marketing for the movie. "Knocked Up" is released June 1st, and "Superbad" comes out a few months later. The whole thing is a takeoff on the David O Russel/Lily Tomlin shakeup from "I Heart Huckabees".
Feeling manipulated yet?