"yass king" means: The highest hype title you can bestow on a man who is absolutely eating — 'yass king' is enthusiastic, theatrical affirmation that someone i.... This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.