Narcissistic insults stem from clashes with reality. Reality sends the message: “You’re not as great or powerful as you think you are.” But grandiose characters don’t take such challenges lying down. They see them as both and affront and an insult. And that’s typically when they unleash their rage.
Narcissistic grandiosity is mostly a matter of exaggeration – especially exaggerated self-importance and capability. And, when such grandiosity goes unchecked, it can lead to much bigger problems.