NPD or Something Else

It helps us to recognize what's really going on with a person who's displaying behaviors that could be construed as abusive or Narcissistic.
If they are actually "NPD", then we really need to be very careful about interacting with them, how much access they have to us and others in our lives, and our resources. A person with NPD is not at all connected to reality, and has apparently no remorse or guilt about getting their wants met, and their wants could range from getting an ice cream right now, to buying whatever toy they want regardless of who's money they're using, to hiding seriously dangerous, illegal, or damaging behavior. As in, they'll set up a Meth Lab in your basement, where you live with your children.
They'll make sure you get fired to retaliate against something that tweaked their ego, or something you didn't even do. They'll trash anyone at all to High Heaven, just for a desired outcome for themselves, or even just for fun, because they're getting attention. They'll tell your parents, your kids, your friends, family, coworkers, boss, neighbors, anyone who will listen that you're secretly a drug-smuggling child-trafficker, or whatever it takes, in order to turn them against you, and to make you lose your support network, business, and reputation. They'll fight for sole custody of your kids, sue you, and try to make sure you don't get your own money or possessions for no reason other than to "win" against you, hurt you, and control you, literally.

Most people who display Narcissism traits or abusive behavior are not "NPD". There's a large number of things that can cause a person to become hostile or abusive, including legal medication, or self-medicating with any kind of substance. (If a person can ingest it and it's for purposes of causing some kind of effect, it's a drug.) Addiction to our own adrenaline and neurochemicals can also cause all kinds of behaviors. Obviously PTSD can cause hostility and defensiveness. BPD can display as aggressive or manipulative behavior, but it's not NPD, and can be treated very effectively, since it's really an effect of control, neglect, and/or abuse on a child growing up. People with Bipolar disorder may have delusions, and may become very aggressive. Alzheimer's is a big one, and tragic, but if you didn't know a person had it, you might think they were a "raging Narc.". A lot of people mistake Asperger's for Narcissism, for various reasons.

If YOU are worried that you're too judgmental, hostile, aggressive, or self-centered, then you probably don't have NPD (you wouldn't CARE if you did, or notice it). But you may benefit greatly from doing research about your symptoms, and finding a good therapist, doctor, or healer.