"It's about me."
There is a lie that people in their twenties learn about the hard way. It turns out that success in school does not guarantee success in career. Even after graduation, it takes hard work and an acceptance of reality in order to be able to move up the career totem pole. For Hannah, this is a lesson that she is slowly learning. "Leave Me Alone" is about the consequence of this belief coupled with being an aspiring professional writer.
This is what happens when you graduate with a useless liberal arts degree. You end up in debt. You end up trying to escape your lousy entry level job. You are qualified to do nothing. The only thing that keeps you going is the internalization that your liberal arts degree investment is going to one day get you somewhere. This all applies to Hannah, except she is unemployed, freeloading off Marnie, and watching (what she perceives to be) a less deserving person get a break in life, in the form of a book deal.
That is the next point this episode made. It mocked the whole writer and reader thing. The episode made it look like writers are self-centered, and have a need for everybody to read and hear about their one of a kind observations, expressions of deep emotions, and dramatic lessons accumulated through life experience. Most writers (that are not good enough to be employed by ShowbizMonkeys) are like this. They enjoy flaunting their self-importance and stereotypical (writer) feelings in their written material, that come from retreating from people and into the unengaging realm of text. Ray commented on Hannah writing about herself: there is nothing more trivial than writing about the fear of intimacy.
To somebody that has to put up with the daily grind of a real job, this made perfect sense. But not to Hannah, since she still believes in that whole writer thing.
The consequences of Hannah's life decisions also caught up with her at home. In this case, with her roommate, Marnie, who had been covering all the bills due to Hannah's non-existing income.
Their spat was not necessarily an outcome of Hannah's career pursuit. It was more like Hannah's self-centeredness created problems not just in career pursuit, but also in her personal life. Hannah seeing that Marnie had bought a copy of "Leave Me Alone," started an argument that got petty, with both women pretending to take the high road. In the case of Hannah, her persecution complex was confirmed to be true, as she would not shut up about finding out what was wrong, and in the process, antagonized Marnie further, and demonstrated a self-fulfilling prophecy coming to life. This was five straight minutes of dialogue, that revealed a lot of things about both Hannah and Marnie, and the nature of their friendship. Hannah had pried open a reluctant conversation from Marnie, and she ended up getting more than she bargainned for. At the end, the two of them decided to stop living together, and storm off to their rooms.