One of things about narcissists which I find baffling is the things which do not bother them. This goes back to their complete lack of empathy, but still, it is astonishing to watch.
If I'm dealing with a narcissist who has no trouble falling asleep anytime or anywhere, then I could understand why they would have little regard for other people's sleep. If they have a partner who struggles with insomnia, they might thoughtlessly be noisy or wake someone up for no good reason, but you might understand why they wouldn't "get" that this is a problem if it's not a problem for them.
What flabbergasts me is the narcissist who is oblivious to someone struggling with the same problem they have. For example, you have a narcissist with insomnia. They struggle to get to sleep. They struggle to stay asleep. They will tear someone's head off for waking them up or making noise when they are trying to get to sleep.
I would expect them to be as considerate of other people trying to sleep as they expect others to be of them, right? Not on your life. Not a narcissist. I know a narcissist who has this problem sleeping. But what does she do? She vacuums, loudly, outside the bedroom door. She wakes them up for trivial things. She bangs and clangs when they're trying to sleep. It's mind boggling to me that she can be so oblivious to someone else trying to sleep when she; 1) has such a hard time herself and 2) demands that other people tiptoe around her sleep.
I know another narcissist who cannot be still and cannot be closed in. What does she do with her animals? Keeps them in little, closed in pens. Again, if she preferred to be in little, confined spaces I might understand her oblivion to its effect on others. But she cannot tolerate it. Yet this is what she does to others.
Their complete oblivion to the feelings of others is stunning. It stems from their complete lack of empathy. And this is one of the ways you will know them.