Former gymnast Nastia Liukin is pissing on the people who helped make her a star after the Olympics, and she's doing it just to launch her own business ... according to her ex-agent.
Liukin -- a gold medalist in Beijing and former "Dancing With the Stars" contestant -- started the beef when she recently said her former reps never got her deals she could be "passionate about." In other words ... they all sucked.
One of those former reps, Evan Morgenstein, took the comment very personally, and tells TMZ Sports ... "It's an absolute slap in the face. She's got revisionist history. She got deals that no other Olympians had ever gotten."
Morgenstein says he was Nastia's agent from '07-'12, and scored her countless lucrative deals -- including JCPenney and Wheaties. He says he always saw Nastia as family and not just a client, telling us ... "My daughters looked up to her."
Liukin obviously thinks she can do better -- she recently opened the Shine Agency.
Morgenstein's not exactly wishing her good luck -- "She had a come to Jesus moment, and now she thinks she's the next Scott Boras. It's ridiculous."
We reached out to Nastia, but no response yet.