I see people through this "they are a narcissist" label at anyone doing anything they don't like.

Narcissistic Personality Disorder is actually a very rare neurological disorder. It develops in childhood through a lack of self-regulation properly developing in one domain, which has a domino effect of negatively impacting the regulation of a second and so on. Due to the impact on pro social domains, this affects an individual's ability to empathize and properly form bonds, to such a deep level that the affected individual cannot produce certain chemicals that a neurotypical will excrete during a bonding process. This is why they can very easily discard. As a result of this lack of self-regulation in multiple domains, the individual may be assessed to exhibit enough personality traits present on the "cluster b" spectrum in order to be diagnosed with it.

Again, it is a very rare condition. The brain of the affected individual developed their neural networks during childhood in a disordered way. Not everyone who ever does anything you don't like is a "narcissist". It would be like calling anyone you like "bipolar", or "schizophrenic". I'm sure you'd appreciate not being called schizophrenic.