"cap mode" means: Someone in cap mode has fully committed to lying — not slipping up once, but operating on a sustained frequency of dishonesty, exaggeration.... 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.