Narcissistic Personality Disorder (NPD) is a pattern of self-centered or egotistical behavior that shows up in thinking and behavior in a lot of different situations and activities. People with NPD won't (or can't) change their behavior even when it causes problems at work or when other people complain about the way they act, or when their behavior causes a lot of emotional distress to others (or themselves? Narcissists never admit to being distressed by their own behavior -- they always blame other people for any problems).
This pattern of self-centered or egotistical behavior is not caused by current drug or alcohol use, head injury, acute psychotic episodes, or any other illness, but has been going on steadily at least since adolescence or early adulthood.
They want praise, compliments, deference, and expressions of envy all the time, and they want to be told that everything they do is better than what others can do.
Sincerity is not an issue here; all that matter are frequency and volume. Narcissists use other people to get what they want without caring about the cost to the other people.
They are unwilling to recognize or sympathize with other people's feelings and needs. They "tune out" when other people want to talk about their own problems.
They show arrogant, haughty, patronizing, or contemptuous behaviors or attitudes.
That and the Sociopath diagnosis you’ve posted before are right on.