It isn't hard to see what Iron Man is thinking. At any given point, Robert Downey Jr lets us inside his character's head to show us how Tony Stark thinks, and this - the visible personality, the unmistakability brought by each actor to each character - might be the greatest superpower of the Marvel movies. Most of their actors are now excellent at this, but Downey set the tone back in 2008 with the first Iron Man, and he remains arguably the best at comic-book acting, emoting minus a thought bubble. His eyebrows are his exposition.
Therefore, in Avengers: Infinity War, when this vain overachiever talks about giving up dairy yet succumbing to ice cream after Ben & Jerry named a flavour after him, it makes sense. Downey delivers the line in that exquisitely offhand way, always making wisecracks appear genuinely improvised, and the moment flaunts his hubris. It is a satisfying moment, swiftly giving us a glimpse at what makes this particular Avenger matter, why he stands apart from the rest of his spandex-wearing peers, and it is definitively true to character.