"black don't crack" comes from African-American Vernacular English or Multicultural London English and means people of african descent tend to wrinkle less with age than people with lighter skin. It has spread well beyond its origin through hip-hop, drill, TikTok and gaming, so a teen of any background may use it. It is not in itself a sign of bad behaviour; it is a style of speech the way 'cool' or 'wicked' once was. The conversation worth having is about respecting where the language comes from, not about banning the word.