This is our Spiritual Guidance on helping people having 'difficult behaviour' overcome their weakness.
Clarification:Narcissistic personality is nothing but a desire/expectation of excessive admiration, attention and being self centred. This comes into behaviour only when you constantly become an object of ridicule from people/souls close in your relationship circle. This leaves such impressions on soul with course of time.
Understand, that we ourselves are responsible for this behaviour of theirs and they need our help. If not taken care conservatively, it may lead to a Personality Disorder.
Now, coming down to "How to deal with it?"
It is honestly not difficult to deal, but requires patience and time with a little love and acceptance.
Sanskars can be changed. Recognise and exercise our original nature, our innate powers > 'Power of Tolerance' and 'Power of Acceptance'... Practice these virtues or say powers in every relationship.
Send blessings... and have good feelings for that soul and help him/her to overcome this weakness.