Two techniques for dealing with narcissists which people have shared with me and I have found helpful are "Medium Chill" and "Robot Mode". There is a lot of overlap in the two concepts. I present them both because most people identify more easily with one than the other. Take what you like.
I cannot find a good description of Medium Chill on the web which is openly accessible. Basically, Medium Chill is a technique for dealing with narcissists. Some people advocate it for life in general. That is not my recommendation. I only recommend this as a strategy for dealing with narcissistic abuse.
Basically, Medium Chill is something you utilize to allow the narcissist's attempts to get inside your head to flow over you without effect. You want to wall off your emotional responses and protect them from manipulation. Maintain a flat expression, or perhaps even a vaguely pleasant expression and block off your emotions so they have no way of telling that they're having an effect - and chill.
The theory behind Medium Chill is that a narcissist's goal is to provoke an emotional response from you. They crave having power over you and seeing the disruption to your mind that they're able to exercise. They emotionally manipulate you to get an emotional response from you. And it doesn't matter what the emotional response is. A fight is as good as a cheer of encouragement, a screaming curse as good as a flowery compliment. They just want a reaction. They just want attention. And they do not care how much it upsets you or affects you because they have no empathy. It's all about them.
Provoking an outburst from you also allows them to write you off - to themselves and others - as the crazy one. You are the one behaving badly. All they said was... and you just went off!
However, give them no outward sign that you're affected by their manipulations and they move on to someone more easily manipulated.
Robot Mode works much the same. I do not advocate the use of either method as a way of manipulating narcissists or as an offensive move, only as a defense. The best thing is to get away from them. If you can't, Robot Mode may be helpful to protect yourself.
It consists primarily of locking away your emotions and intellectualizing about what is happening between you and the narcissist - instead of feeling it. You must realize that the narcissist is reading your emotions and calculating responses based upon what they read. If you stop thinking about what your feeling and block off your emotions from the predatory narcissist, then you are free to analyze what is happening with a cool and detached mind and make better decisions about how to respond - or not to respond.
Remember, the narcissist is an emotional manipulator whose goal is to provoke you to react, or even better, overreact. Then they can derail you from the point you were trying to make, or the bad behavior which you were confronting them about, or the boundary you were trying to set. If they can provoke you to behave badly enough, they can cast you as the crazy one.
Also remember that a narcissist's emotions are very limited and very shallow. They feel no empathy and no remorse. (I have been told they only experience fear and anger. I have not seen this disproven yet.) Given that they experience no empathy and no remorse, trying to "connect" with them is futile. If someone feels no remorse and no empathy, what is there to connect with??? Because their emotions are extremely limited, or non-existent, they view people who have emotions as being "weak" and easily manipulated. They resent the fact that you feel and realize there is something missing in them because they do not. But they will never own this, nor are most of them even conscious of it themselves. This is what is happening on the subconscious level. Consciously, they just sneer at you for being so "weak" and get off on exerting their power over you by manipulating your emotions.
Also, because they experience no remorse, they are not bound by conscience, morality, ideals, principles or "doing the right thing". They are not loyal friends, lovers or parents. They are not fair bosses. The right thing for a narcissist is whatever suits them at the moment. What effect that will have on others is absolutely unimportant to the narcissist. It's all about them and what they want. How do you interact with someone like that? Robot Mode.
By putting your emotions out of reach and blocking them off you take away their ammunition against you. They are unable to "read" you. By cutting off your emotions, you are now on the same playing field with them. You can coldly calculate your next move, just as they do. You are now talking to a Robot as a Robot. Robots don't emote. They don't react. Robots don't care. Robots can't be guilted, or shamed, or bullied.