I'm just going to say it: I don't like Joss Whedon. I don't like the way he writes characters, I don't like how insufferably smug his "wit" is, I don't like how interchangeable any characters from any of his works are with any characters from any of his other works and I especially don't like how, rather than having actual relationships, all his characters ever seem to do is posture with each other.
Case in point, Captain America's line in the Avengers trailer: "Big man in a suit. Take that away and what are you?" Now, I'm not big on the comic history, so I can't comment on that, but based on what I've seen of the movies, I can understand Cap not liking to Tony Stark much. Cap is a responsible, properly morally aligned relic from an age when politeness was much more strongly expected of people, while Tony is a smug, self-satisfying businessman whose attempts to learn genuine responsibility haven't quite taken effect yet. Yes, I can see the two not quite getting on well at first, but based on the way he was portrayed in his movie, I cannot see Steve Rogers saying something so fratboy douchebaggy as "Big man in a suit. Take that away, what are you?" As if he need to prove something to himself by demeaning Stark.
That is, however, the only way that Joss Whedon knows how to write character interactions.