Rockets, Communists, and the Dewey Decimal System - S1-E2
Other mistake: As Young Sheldon is a prequel series to Big Bang Theory, this episode is at odds with episode 2-13 of Big Bang Theory, "The Friendship Algorithm," in which Sheldon is unfamiliar with books like "How to Make Friends and Influence People," which he reads in this episode of Young Sheldon, produced nine years later but taking place twenty years earlier.
Answer: Some people just have a dislike for someone that can't be explained. Could be as simple as the way he's dressed.