One of the key aspects of Tony Stark's personality in the comic books is his tendency to turn to alcohol. That's something that hasn't really been explored in previous Iron Man movies and it's about time that it was. Stark got drunk in Iron Man 2, believing himself to be dying (wearing the Mark IV suit, nonetheless), but that's about all we've seen to suggest that he has any kind of problem with the addictive substance. His emotional turmoil in Iron Man 3 would suggest he's in a fragile mental state and the events of the upcoming Avengers: Age of Ultron - which many believe could turn out to be Tony Stark's fault - could drive him to the drink in a serious way. He was already looking to Bruce Banner for a little bit of friendly counselling in the Iron Man 3 post-credits scene, so a downward spiral does seem somewhat inevitable.
