I'm very skeptical of a lot of the diagnoses around me. A friend of mine, let's call her Jissanthepuss, is diagnosed depressive, underwent elective electro-shock therapy, and is prescribed a galaxy of little pills.

I'm convinced that she's secretly suffering from narcissistic personality disorder. She's a narcissist. This author puts it well

A quick primer on the new Narcissism.

I don't mean the traditional Kernberg, Kohut, or even Freudian descriptions. In the modern times, I think narcissism has evolved.

A narcissist isn't necessarily an egotist, someone who thinks they are the best. A quick screen is an inability to appreciate that other people exist, and have thoughts, feelings, and actions unrelated to the narcissist. These thoughts don't have to be good ones, but they have to be linked to the narcissist. ("I'm going to get some gas-- because that jerk never fills the car.")

The narcissist believes he is the main character in his own movie. Everyone else has a supporting role-- everyone around him becomes a "type." You know how in every romantic comedy, there's always the funny friend who helpes the main character figure out her relationship? In the movie, her whole existence is to be there fore the main character. But in real life, that funny friend has her own life; she might even be the main character in her own movie, right? Well the narcissist wouldn't be able to grasp that. Her friends are always supporting characters, that can be called at any hour of the night, that will always be interested in what she is wearing, or what she did. That funny friend isn't just being kind, she doesn't just want to help-- she's personally interested in the narcissist's life. Of course she is.

A comedian I can't remember made a joke about actors in LA, but it's applicable to narcissists: when two narcissists go out, they just wait for the other person's mouth to stop moving so they can talk about themselves.

So on the one hand, the narcissist reduces everyone else to a type, as it relates to himself; on the other hand, the narcissist, as the main character in his movie, has an identity that he wants (i.e. he made it up) and requires all others to supplement that identity.

I agree with the OP's post that there is a total over reliance on some diagnoses. I don't think they're rigorously made.