The actor and All-American Rejects singer said on a recent podcast appearance that Kelly, whose real name is Colson Baker, became "fully unhinged" and went "ballistic" on him when Ritter was discussing a movie scene with his costar Megan Fox, who happens to be MGK's fiancée.
"We're on set and I go over to Megan's trailer because in the film, there was this scene that she basically teases me, putting my fingers in her mouth," he said. "So I walked over to her and wanted to discuss this moment where a monster rips out her f---ing heart. That's her death scene."
Shawn Goldberg/WireImage; Taylor Hill/WireImage Tyson Ritter and Machine Gun Kelly
He continued: "I go over there and I was like, 'Hey, Megan, I wanted to talk to you about this moment where, when you die, because you've been teasing putting my fingers in your mouth, that when you're dead, I put my fingers in your mouth,' and it's sort of like this resolution to my character getting his revenge."
To hear Ritter tell it, Kelly didn't appreciate the suggestion. "Colson just goes from zero to awesome rage and awesome super angry," he said. "He was super bummed about me asking if I could put my fingers in Megan Fox's mouth… He just went ballistic. It kind of went maniac mode."
Ritter, however, wasn't particularly fazed by the rapper's reaction. Instead, he was inspired. While making Johnny & Clyde, he was also working on Prisoner's Daughter, in which he portrays an abusive addict, and apparently Kelly demonstrated the energy he was seeking for his character. "It's funny, man, I just kind of held the space for it and I was like, 'This is what I've been looking for with my character on Prisoner's Daughter,'" he recalled. "That was the greatest gift for my role in the other film."
Dubbing Kelly "Pistol Pete," Ritter added, "I remember when [he] just started going ape on me, I was like, this is really confrontational, but also like, thank you, dude. He might've been having a bad day, but I'll never forget, a lot of my role, in that one moment especially, it's not only my dad being his drunkest, wildest self, it was a little bit of Pistol Pete in my role for Prisoner's Daughter."
As for Fox, Ritter had nothing but praise for the actress, calling her "a sweetheart to work with."
Representatives for Fox and Kelly didn't immediately respond to EW's request for comment.