The Iron Man 2 star was constantly subjected to cruel taunts and harsh criticism from her Air Force military officer stepdad, who married her divorcee mum when she was just two years old.
Munn has largely kept her troubled childhood a secret since finding fame, but she's now opened up about the emotional pain she endured as she was growing up in a candid new interview with Ocean Drive magazine.
She tells the publication, "He would always say, 'You're not smart enough (to become an actress), pretty enough, you have no talent,' and it would knock me down."
But the 31 year old admits his behaviour did have one positive outcome - it helped her discover her comedic chops.
She adds, "When (my stepfather) would be screaming his head off in the living room, I would hustle everybody into my room and launch into imitations of teachers or do scenes from movies. And that would take their minds off of the hell that was happening down the hall."
Her mother subsequently divorced her second husband when Munn was a teen.