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.