There are two variations of the Silent Treatment that are common in narcissists (and bratty children, who narcissists resemble).
Your Narc ever do either of these things to you? My MN sociopathic ex used to do these things ALL the time whenever I was trying to make an important point and/or defend myself from his abuses. Whenever he did either of these things, I wanted to shove his face through a wall.
1. The Sing-Song Game.

If I was trying to tell him something important, he’d actually stick his fingers in his ears and sing “LALALALALALA!” Like the Silent Treatment, this tactic is an effective way of making you feel not heard, with the added advantage of implying that your message is unimportant or stupid enough to attract such a childish reaction. It’s infuriating–and of course that’s the intention. They’re trying to get a reaction from you, because an emotional reaction (even a negative one) gives them an easy fix of narcissistic supply.
2. The Echo Chamber.

Echolalia (repeating everything you just said) might be even more infuriating than the Sing-Song Game. It’s another thing both children and narcissists love to do to cut down anything you have to say. You say or ask something, and they repeat it. You ask them to stop, and they repeat that. And on into eternity. They may even mock your tone of voice while doing this or your mannerisms. My ex also did this all the time.
You: “I wish you’d chew your food with your mouth closed.”
N: “I wish you’d chew your food with your mouth closed.” (said with mouth full of food)
You: “I asked you not to do that.”
N: “I asked you not to do that.”
You: (sighs)
N: (exaggerated sigh)
You: “Do I have to leave?”
N: “Do I have to leave?”
You: (becoming angry): “STOP IT!”
N: (exaggerating your angry tone of voice): “STOP IT!”
If you respond with silence at this point, you’ll be met with silence too. After all, this is only a variation of the silent treatment. The best thing to do is leave. Nothing you do or say is going to stop them, until they become bored.
3. Smile!

Sometimes, when you’re trying to talk about a serious subject, the narcissist will smile or even giggle inappropriately. Oh, they know you’re being serious, but again this tactic is meant to undercut the seriousness of what you’re trying to say and is intended to annoy or anger you. It’s a simple but effective weapon to kill communication.
Can you think of other infuriating, childish things narcs do to kill communication? I may add them to this post.