Sheldon Cooper's claim that Billy Sparks was a childhood bully on The Big Bang Theory has been revealed as a lie, with Young Sheldon portraying the character in a more positive light. The explanation for this inconsistency may lie in George's near-cheating with Brenda, Billy's mom, which Missy may have shared with Sheldon. In retaliation, Sheldon could have made up the story about Billy being a bully to get back at him and his family. While it remains to be seen if season 7 of Young Sheldon will delve further into this storyline, it provides a plausible explanation for Sheldon's biggest lie.