That last panel is a bit of an homage to David Willis... in his Shortpacked! webcomic he can take a simple little phrase like "I'm Batman" and find endless different ways to get a laugh out of it.
TRANSCRIPTION COURTESY OF JOSEPH HOUK - (CW, listening to the Christian Bale "audio rant" from Terminator: Salvation) "Wow. Why does Christian Bale get so riled over stuff like that?" (MG) "No big surprise. He's been like that for a while now." (CW) "And how would you know?" (MG) "I got on as an extra in a film I always wanted to be in, and I was just busting his balls all the time..." [2004: The set of "Batman Begins"] (Christian Bale, as Batman) "I'm Batman." (MG, in the background) "Hey, it's Gotham-ian Psycho! Ya like playing dress-up, Pat?" (Bale) "CUT!!! Chris, WHAT THE FUCK'S going on here?" [Meta-joke: Bale's rant was because his director kept walking on-screen in the background behind him on the TS set – the same as Matt did.]