Rudd, reprising his role of Scott Lang/Ant-Man, talked about what it was like being the newbie alongside the other superheroes.
"I felt a little bit though like...." Rudd started, before Mackie silenced him with a warning, "Uh!!"
"I felt like they were a fraternity, like 'Animal House,' and I was Flounder," he said, namedropping the character played by Stephen Furst in the comedy.
"And that's why we wanted to trade him for Scarlett Johansson," quipped Stan, who again plays Cap's cybernetic-armed former assassin buddy Bucky Barnes.
"He was on the trading block," joked Mackie, noting Team Cap wasn't able to make the deal to get Black Widow instead. The jabbing was apropos, as the stars revealed an exclusive clip of "Civil War" that shows an obviously geeked-out Lang meeting the spangly hero for the first time.
Rudd said Ant-Man is the first role his children knew he had -- and the same goes for their classmates. "Just, like, last week, I was at my daughter, who's six, her kindergarten class ... parents come in and they talk about what they do ... And I know them all because I go to the school, but they just kept calling me 'Ant-Man.'"
"The problem isn't the kids," Mackie interjected. "The problem is the parents. You know, because the parents, they go, 'Go take a picture with him!' And the kid's like, 'I don't know who that is!'"
Mackie also joked about a pet peeve of his: handsy male fans. "You get some grown man coming up to you and touch your 'sweet spot.'... Don't put your hand on the small of my back!"
Taking sides against Team Cap are Robert Downey Jr. as Tony Stark/Iron Man, Tom Holland as Peter Parker/Spider-Man, Paul Bettany as Vision, Elizabeth Olsen as Wanda Maximoff/Scarlet Witch, Don Cheadle as Col. James Rhodes/War Machine, and Chadwick Boseman as T'Challa/Black Panther.
The film, directed by "Captain America: The Winter Soldier"'s Joe and Anthony Russo, will be released May 6 by Disney, the parent company of ABC News.