I wouldn't say that anything actually happens "to" Gatsby during the Sloane's visit. This scene is more about the quality of people that Tom associates with - the old money people who look down on new money - and the attitudes that they have. When Gatsby invites them to stay foe dinner and Mrs Sloane refuses hastily, ostensibly because she has already been forewarned about Gatsby by Tom or perhaps because she generally distrusts people whose money is not ties to family and social status within the community, she quickly realizes that she has been rude (also something that the rich don;t do toward people who have as much money as they do). She invites Gatsby to dinner, but really does not expect him to accept, nor does she want him to actually come to dine with her. He does accept, but more to prove a point than out of any desire or intention to ever go there. This is a scene of social posturing that illustrates the differences between the Gatsbys of the world (people who came from poverty and made their wealth whether through legal or less than legal means) and old money (those who were born to money and whose families have established status) and it clearly shows why, no matter how rich he becomes, Gatsby will never be "in the same league" as Tom and Daisy.