SPOILER WARNING: We're going to describe in detail what goes down in the post-credits scene of Marvel's Ant-Man. If you haven't seen that teaser yet and/or have no desire to see it, then we suggest skipping this story. However, we have plenty of other wonderful content you would probably enjoy perusing.
Did you go see Ant-Man this past weekend, spent two hours obsessing over the fact that we live in a world where Paul Rudd is an action movie star, and then immediately leave after the end of the movie? Did you not notice 85% of the theater sitting in their seats, waiting? Amateur!
By now you must realize that after every Marvel movie comes at least one vague, slightly-confusing scenes that sets up the next Marvel adventure. Of course, it's only vague and confusing if you don't know what's happening, and that is why we're here now. We're going to explain that post-credits Ant-Man scene so you know how it applies to Captain America: Civil War and how it all relates to the Marvel Cinematic Universe (MCU).
LAST SPOILER WARNING...
In the final, final post-credits scene (we're not talking about the mid-credits scene with Evangeline Lilly and Michael Douglas), Captain America (Chris Evans) and Falcon (Anthony Mackie) are standing in what appears to be a warehouse, and they have an old friend with them: None other than Bucky Barnes/The Winter Soldier (Sebastian Stan). His metal arm is caught in some type of contraption, and he looks defeated. He's either injured, captured or giving up. Or all three.
Earlier in Ant-Man, Scott Lang took on Falcon and won, and the end of the film revealed that the bird of prey was looking for him. Presumably to beat him up…until we got to that end credits scene, and after Cap says they can't call Tony Stark (Robert Downey Jr.) because he might not believe Bucky is alive/not evil anymore, plus "The Accords" wouldn't let him do anything. And that's when Falcon says he "might know a guy" to help out. Probably Ant-Man.
It was a quick scene, but it said so much. First of all, it proved that between Age of Ultron and Ant-Man, they found Bucky and he's no longer with the Hydra team. And second, it set up the rivalry that will no doubt fuel Captain America: Civil War, which is the next film in the Marvel line-up. Captain's reference to "The Accords" and Tony is a nod to the fact that Stark is all for registering superheroes and their identities. Steve is not, which means those two are continuing to butt heads even after Ultron.
Finally, if Falcon wants to recruit Ant-Man to help them out, that probably means that when it comes to Captain America vs. Iron Man, Scott is Team Cap.
TL;DR: Captain America and Iron Man are at odds already. They found Bucky. Ant-Man will probably fight alongside Captain America in Civil War.
Meanwhile, we like to imagine Paul Rudd is talking to the nerds blogging about Ant-Man today like this: