At the apartment, everyone was pretending to be someone they were not. People were very willing to act the part, joining Myrtle and her "boyfriend" for a grand time with dancing and music. However, everyone except for Tom was faking it. Perhaps this is why he got into a fight with Myrtle. Even though he was willing to use her during the affair, she crossed a very well defined line by speaking of Daisy as if she were in the same social class. This is most undoubtedly why he smacked her during the party described in the novel.
At the Buchannan's party, there was no pretending... everyone had money, and it was a known fact. It was, as Amy said, a chance for everyone to show off just how rich and wealthy they really were.
The small dinner party at the Buchanans' is quite elegant, quiet, civilized, and conventional. Dinner by candle light is served outside on a beautiful evening--a lovely picture of the Buchanans at home, except for the interruption by Tom's mistress calling him on the phone. When Tom takes the call inside, Daisy follows him. An argument ensues, but it takes place in controlled, hushed voices. Tom and Daisy return and resume their evening with guests.
The party in New York takes place at the apartment Tom rents in order to carry on his illicit affair with Myrtle Wilson. The apartment is small, crowded, noisy, and filled with cigarette smoke--a very cheap and unpleasant atmosphere. Tom and Myrtle, as well as their guests, are all drinking heavily. When an argument breaks out between Tom and Myrtle, it is not conducted in a "civilized" manner. Instead, a drunken Myrtle taunts him, and he breaks her nose in a split-second, instinctive act of violence.
The Buchanans' party is very formal and haughty. It's old money flaunting itself.
The party at the apartment is new money in a more casual air of someone who hasn't always had money.
In both cases, they are showing their wealth with an abundance of food and drink and opulence.
thanks that was really helpful.:)