In The Great Gatsby, why does Myrtle Wilson behave with such hauteur, both toward her husband and in the city apartment?
Myrtle Wilson is ashamed of her social position in life. She is ashamed that she is married to a poor man who Nick describes as "a blond, spiritless man, anaemic, and faintly handsome." Myrtle tries to compensate for this shame by acting proud. She treats her husband, George, terribly in order to assert herself as being better than him, like a wealthy aristocrat rudely ordering around a servant.
At the apartment, Myrtle is away from that life she is ashamed of. She is with Tom, a more successful man, and feels freer in this situation. She acts with hauteur in this case because she's indulging herself in this, for her, alternative world of higher social status.
Her laughter, her gestures, her assertions became more violently affected moment by moment, and as she expanded the room grew smaller around her, until she seemed to be revolving on a noisy, creaking pivot through the smoky air.
Myrtle changes her clothes when she is at the apartment. This is part of her social change from poor George Wilson's wife to a socialite having cocktails with Tom Buchanan and friends. Myrtle was playing up this role while she could. She was indulging in this alternative to her life with George. It is hard to sympathize with Myrtle because she is unfaithful to George and because she acts so superficially, but she feels trapped in her weary life. This world with Tom is an escape from her drab world in the Valley of Ashes.
In The Great Gatsby, Myrtle Wilson believes she is too good for her husband, George, and belongs in the upper echelons of society with Tom Buchanan. She believes George hoodwinked her into marrying him:
"I married him because I thought he was a gentleman . . . I thought he knew something about breeding, but he wasn't fit to lick my shoe."
She later goes on to describe how she realized how poor George was when marrying her ("He borrowed somebody's best suit to get married in"), and her sister, Catherine, says this is why she feels it's perfectly okay for Myrtle to have a "sweetie" in Tom.
Myrtle's entire apartment is symbolic of her desire to be of a higher social class, but how she doesn't fit—the "tapestried furniture" is too large, the artwork is tacky, and the magazines of Town Tattle suggest an envy of the wealthy in New York.
Contrast Myrtle's desire for luxury and Tom's wealth with George's shop ("unprosperous and bare") and his appearance ("a blond, spiritless man, anemic, and faintly handsome") and it's pretty obvious why she behaves with such hauteur toward her husband.