Not so hard to know, simply watch out for these behaviors in them;
Narcissists always want to be the best, the most right, and the most competent; do everything their way, own everything, and control everyone. They simply want to be on top of game all the time.

Narcissists always demand attention from others. Not like they really need the validation or something, they just want that want all attention to be on them all the time.

Narcissists are perfectionists — extreme perfectionists. You can spot a narcissist through their extremely hneed for everything to be perfect. They want to be perfect, things and people around them to be perfect, his is not always possible which results in the narcissist feeling dissatisfied and miserable much of the time. The demand for perfection leads the narcissist to complain and be constantly dissatisfied.

Lack of responsibility is another obvious sign of a narcissist. Although narcissists want to be in control, they never want to be responsible for the results—unless everything goes exactly their way and their desired result occurs. When things don’t go according to their plan or they feel less than perfect, the narcissist places all the blame and responsibility on another person. It has to be someone else’s fault.

Narcissists do not show empathy nor do they truly understand how others feel. Because of their inability to understand feelings, their lack of empathy, and constant need for self-protection, narcissists can’t truly love or connect emotionally with other people. They cannot look at the world from anyone else’s perspective.