When someone says in public, "they know everything," it is not necessarily indicative of a grandiose delusion. Instead, it is more likely to be a figure of speech or a colloquial expression commonly used in everyday conversations. People often use such phrases in a non-literal sense to convey various meanings, such as:
Hyperbole: Exaggeration is a common rhetorical device used to emphasize a point. Saying "they know everything" might mean that the person being referred to is knowledgeable or well-informed on a particular topic.
Frustration or irritation: People may use this phrase to express frustration or annoyance with someone who acts like they know everything or is arrogant about their knowledge.
Humor: It can be used humorously to poke fun at someone's perceived know-it-all attitude or to mockingly praise their vast knowledge.
Sarcasm: In some cases, the statement may be sarcastic, implying that the person being referred to claims to know everything but might not actually possess such knowledge.
While grandiose delusions do exist and are associated with certain mental health conditions, like narcissistic personality disorder or some forms of psychosis, a simple statement like "they know everything" in public is unlikely to be a clear indicator of such a condition.
In general, people use language creatively, and phrases like this are part of how we communicate and convey meaning in different social situations. It is essential to consider the context and the individual's overall behavior and communication patterns to understand the intended meaning fully.