Narcissism is characterized by a few fundamental traits that set it apart from other personality disorders. Perhaps easiest to see in the narcissist is that they are developmentally stunted individuals who can be of any chronological age but behave in ways that make them seem much younger, typically like toddlers, young children, or young adolescents. In short, they are grown adults who are more like children.
We all get cranky and need to take a nap sometimes. But they "are like children" in very fundamental ways, such as, seeing things from only their point of view; having little to no self-awareness; and lacking true empathy (here defined as being able to understand and connect with other people's feelings, thoughts, and actions). We've all seen the type at work, at school, in our families, and out there in the world.
Another related, fundamental character trait of narcissists is that, as adults living out a sentence of arrested development that began at a much younger age, they're not really people. It's not that they're aliens or nonhumans; they are biologically human beings like me and........