Blanche's fear of reality is her biggest enemy in Tennessee Williams's A Streetcar Named Desire.
Blanche is a woman who has grown up in privilege only to drop down to utter poverty and debauchery at an age where she could have still found a good man who would support her. However, Blanche's lack of strength confronting the loss of her family plantation, the suicide of her husband ( as well as his homosexuality), and the loss of her teaching license (due to a scandal), make her mask her pain with alcohol. Once she is inebriated, she can create an artificial fantasy where there are still gentlemen callers wanting to attend to her needs. However, we know that Blanche is a broken woman, far from the Southern belle that she still tries to pass for in front of men.
Her fear of the realities of her life make Blanche adopt a persona which aggravates those who notice how fake it really is. That is what occurs with Stanley, who is able to detect the rarity of Blanche's talk and pose and immediately went for clues as to what she could be hiding. Blanche over-dresses as if to hide the fact that men would find her to be a low woman, and she uses her charms in a way that comes out looking like she is plainly asking for trouble.
But worst of all are her "spells", when the light focuses on her and she remembers her dead husband. How she finds him in bed with another man, how she tries to push it down as if nothing has happened and how, in a snap, she says words to him so cruel that he shoots himself. That alienates her as well, for she has never been able to get over it. Also it drives her to drink even more and continue with her vicious cycle.
In all Blanche's behavior alienate her from people who are simply trying to lead normal lives the best way they can. She imposes upon people, drinks too much to forget, and her sensuality is overused. This is enough to make everyone around her to feel uncomfortable and out of place.