The 29-year-old actress and her friends have each other's backs -- so much so, that a bad breakup with one of them could leave you with an egged car.
While speaking with ET's Rachel Smith at the London press day for her upcoming movie, Birds of Prey (and the Fantabulous Emancipation of One Harley Quinn), Robbie revealed that she hasn't done anything "quite as dramatic" as the stages of breakup that her character, Harley, goes through in the movie -- but she has another experience with her girl squad.
"I do have a wonderful group of girlfriends back in Australia -- we've been friends since we were like four years old, and anytime a dude breaks up with a girl in the group, all the girls go and egg his car," she revealed.
"That's amazing!" Robbie's co-star, Chris Messina, marveled.
"One time I broke up with a boyfriend, and they were like, 'How dare he! We're going to go egg him!' And I was like, 'No, don't! I broke up with him. He's a really nice person. Please don't egg his car!'" the actress recalled with a laugh. "'Thank you, I love you guys, but don't do that.'"
Robbie reprises her role as Harley Quinn in the Suicide Squad spinoff Birds of Prey, which sees the character join forces with Black Canary, Helena Bertinelli, and Renee Montoya to save Cassandra Cain from Gotham City crime lord Black Mask. The Australian actress also serves as producer, after having pitched the idea for Birds of Prey to Warner Bros. in 2015.
"I'm just so happy that the movie's finally about to come out. I feel like it's been a pretty long road to get here and at points I was like it's never gonna happen. I just can't get it up over the line," Robbie told ET.
"It was a pretty risky proposition when I first pitched it four and a half years ago. I put the pitch together and I was saying, 'I think we should do a female ensemble action film with an R rating,' and that sounded like an insane thing to do," she said. "I could totally understand everyone's hesitation and then movies like Deadpool started coming out and proving that you can do an R rating in the comic books base and be successful."
"I feel like there's such a positive response to something new and fresh and different and people are really hungry to see something they haven't seen before, particularly in this day and age," Robbie added. "So, I feel like all those things help to kinda get this film up and running and now I'm just stoked it's gonna be out in the world."
Ella Jay Basco, who plays Cassandra Cain in the movie, couldn't be more excited. "This is my first big feature film, and for it to be like this ginormous Harley Quinn DC movie is crazy," she expressed. "I honestly... I still can't believe it, it feels like one long dream. Like, someone needs to pinch me awake."
Birds of Prey hits theaters on Feb. 7. See more in the video below.