what do you think Fitzgerald wishes to convey about Gatsby parties through the incident with the drunks and the car and the husbands and wives arguing?

Fitzgerald wants to convey the fact that the people that go to Gatsby's parties have no interest in their host or really anybody else. They get drunk and then display a very superficial childish behavior. They clearly lack any kind of self-discipline or moral clarity. It is a snapshot of the excess and vacuous nature of the people that inhabit Gatsby's parties.