While Elon's then-partner Grimes was recording her part in the game as cyborg popstar Lizzy Wizzy, the erratic tech billionaire turned up with an antique firearm to "insist" on being included in the game. "The studio guys were like sweating," Grimes is quoted as saying. Musk adds "I told them that I was armed but not dangerous".
Apparently, the developers relented at the time, though it's unclear if Musk did actually get the cameo in the end.
Some people believe he showed up briefly in one scene in the background but it was never substantiated.