Captain America: Language!
The first word out of Captain America's mouth in this movie is a scolding. Iron Man has just dropped an S-bomb, which apparently in Cap's view is the only bomb he doesn't approve of his teammate dropping.
This says a lot about the pair's relationship, as well how Captain America functions on the team—both for better and, let's face it, for worse. Let's take a closer look at what we mean by both of those things (we promise not to swear—too much):
It's more than just a clever name—Cap is the leader of the Avengers. He makes the battle plans, he delivers the motivational speeches, and he also makes sure that the chore wheel gets updated on a regular basis.
In other words, dude is a bit of a control freak.
In some ways, this is understandable. The guy is coming from a military background where everything is stamped in triplicate and organized in a very top-down fashion, with superiors and subordinates all knowing their place—and the consequences for screwing up.
Still, for all the explosions they cause, the Avengers are about as far from the military as you can get. They're all strong-willed, super-powered, and self-directed. Trying to get them on the same page is a bit like wrangling kittens—if kittens could, you know, fly around and call down lightning from the sky. (Say—that gives us an idea for a new comic book.)
That goes roughly triple for Tony Stark, so it's no surprise that Iron Man and Captain America butt heads quite often during the course of the movie. Specifically, Cap is bent out of shape that Tony never bothered to mention that he was developing Ultron. What's worse, Tony tries it a second time with J.A.R.V.I.S. and Ultron's android. When Cap catches wind of this, he blows a button on his uniform:
Captain America: I'm gonna say this once.
Tony Stark: How about nonce?
Captain America: Shut it down.
Tony Stark: Nope, not gonna happen.
Things are tense, and then they get tenser. Luckily, Thor shows up and zaps Vision before Cap and Iron Man can throw down with any degree of seriousness. Still, this skirmish shows how much Captain America wants to be in control of his team as their leader, and how much it sticks in his craw when one of the Avengers deviates from that script.
All the same, the Captain's focus stays on his team, not himself. He preaches the gospel of togetherness, perhaps in part to account for just how mis-matched his team really is. An irradiated anger beast and a Norse god just don't have all that much in common.
Yet, somehow, the Avengers hang together. And Captain America's attitude is a big part of that:
Tony Stark: How were you guys planning on beating that?
Captain America: Together.
Tony Stark: We'll lose.
Captain America: Then we'll do that together, too.
In victory or defeat, Cap's vision for the team is one of unity at all times. It's almost as if he's enabling the heroes to work together through sheer force of will. Just look at how he gets them ready for the final assault of Ultron's Iron Legion bots:
Captain America: The rest of us have one job: tear these things apart. You get hurt? Hurt 'em back. You get killed? Walk it off.
Now if that's not a pep talk, we don't know what is. Consider us pumped. There's a reason why he's the one that gets to say "Avengers assemble!"