In The Avengers, despite the mess Hulk made with the ship, why was the Iron Man so sure that Dr. Banner would return to fight?
Stark is shown to have taken a liking to Banner, and in their talks aboard the helicarrier, he encourages Banner to "suit up" with the rest of them.
I suppose it could be argued that Iron Man is such a good judge of character that he innately knew that Banner wouldn't let them down, but this being the arrogant Tony Stark, I think it's more likely that this confidence stems from his self-assurance, i.e. he was convinced that his little pep talk with Banner would work.