He is Tony Stark. Tony Stark is him. That's his personality. Most of what he says in the movie, wasn't written that way, he just said it. The blueberries in The Avengers, wasn't planned. He gets hungry on set, so he hides food everywhere. For a while they would re-film any scene that he pulled out hidden food, but Jon Favreau eventually gave up and let him have his food in the movie. The blueberries were tapped under the desk he was behind, and he just took them from under there and started eating them. None of it was scripted. Unless he's at a table eating on a plate, the food wasn't planned (in any of his movies).