Meaning:

Short for the English term “narcissistic personality disorder,” it refers to a mental health condition in which people have an unreasonably high sense of their own importance. They need and seek too much attention and want people to admire them. People with this disorder may lack the ability to understand or care about the feelings of others. But behind this mask of extreme confidence, they are not sure of their self-worth and are easily upset by the slightest criticism. Chinese netizens use it in a more general sense to describe people who are narcissistic or selfish.

Example:

A: 你们新来的领导人怎么样？

Nǐmen xīnlái de lǐngdǎo rén zěnmeyàng？

How would you describe your new boss?

B: 大概是个NPD，平时很冷淡的样子，只有听到别人的奉承时才会笑容满面。

Dàgài shì ge NPD，píngshí hěn lěngdàn de yàngzi， zhǐyǒu tīngdào biérén de fèngchéng shí cái huì xiàoróng mǎnmiàn。

I suspect he has NPD. He often comes across as cold and aloof, only showing warmth when he’s being flattered.