playground rumor

noun2

1. •
   An imaginative rumor, misconception, or urban legend spread among children, or regarded as similarly unconvincing.

   • In what sounds like an elementary school playground rumor, a TikTok dentist has warned her followers that cavities can spread by kissing. — 2022
2. •
   An unverifiable claim of hidden or unlockable content in a video game (especially associated with the late 1990s, before the Internet trivialized debunking such claims).