Coming from a background in psychology, I tend to view most all things from a psychological standpoint. I tend to point out the cognitive or biological bases for the reasons that people behave the way they do. It is obvious that Blanche DuBois, played by Vivien Leigh) in Eliza Kazan's 1951 film, A Streetcar Named Desire, based on Tennessee Williams' 1947 play, suffered from some mental disease--the question is what exactly it was. Perhaps she was suffering from a case of Post Traumatic Stress Syndrome from her traumatic experience of losing her husband twice at such a young age--once from his committing adultery with another man and again from his fatally shooting himself. This could very well be argued as the case, but I have an alternate suggestion. Perhaps it was something else, something that some might just see as a personality quirk, or a tough case of conceitedness--perhaps--but I think that Blanche suffered from a case of narcissism.
Narcissism as defined by The American Heritage® Dictionary of the English Language (Fourth Edition) is as follows: "excessive love or admiration of oneself; a psychological condition characterized by self-preoccupation, lack of empathy, and unconscious deficits in self-esteem; erotic pleasure derived from contemplation or admiration of one's own body or self, especially as a fixation on or a regression to an infantile stage of development; and the attribute of the human psyche characterized by admiration of oneself but within normal limits."
At the end of the film, we know that Blanche was escorted to an insane asylum, but was this punishment merited? According to this definition, I would say yes because Blanche did have a mental disorder. This would also explain the trouble she had brought along with her to her sister's, Stella Kowalski (played by Kim Hunter), house. Even in the very beginning of the film when Blanche has become reunited after some time with Stella, within her first few breaths, she started talking about how good she looked compared to Stella. Blanche's actions of constant flirtation, especially with Marlon Brando's Stanley, and obsession with herself ultimately led to her downfall.