It looks like Joseph got word that his other interview didnt come across as excited. Maybe the producers told him to promote it a little better. It comes across as a in your face kind of thing.
I think he probably heard everyone complaining that he wasn't excited and taking the film seriously. To be honest, if I was in his shoes, I'd probably do the exact same thing (I'm a smart-a** like that)
I saw this before and I think people are too hard on the guy, I happen to believe him. He doesn't strike me as the type to take a role just to be in the next big thing. He seems like a laid back kinda guy anyway, just because he doesn't do cartwheels in front of every interviewer doesn't mean he has little interest in the role.
If I were him I'd just wear a size triple-X shirt that says "I AM REALLY EXCITED ABOUT GI JOE, BITCH" just to mock everybody who was over analyzing his last interview.