John Updike delays his dramatic conflict in his story "A&P" until two-thirds of the narrative is finished. This delay allows the author to have the development of Sammy's infatuation reach its romantic illusions: "Poor kids, I began to feel sorry for them, they couldn't help it." Thus, when Lengel confronts the girls about their attire, Sammy is convinced of his decision as well:
"...this isn't the beach."
He didn't like my smiling--as I say he doesn't miss much--but he concentrates on giving the girls that Suday-school-erperintendent stare.....
"We want you decently dressed when you come in here."
Sammy quits because he feels he must protect the honor of his girlfriends and because he is boisterous and rebellious and he can no longer stand the lack of character in the customers. In addition, Sammy feels,
once you begin a gesture it's fatal not to go through with it.
That his gesture is meaningless as the girls have left, makes it a dramatic conflict as well as all the more heroic since it also arises from selfish impulses--he wants to get the attention of the girls, and take it away from them. Instead, he arrives in a sort of limbo,
...my stomach kind of fell as I felt how hard the world was going to be to me hereafter.
To best answer this question, it is important to know what "dramatic conflict" is, and once you know, if you are familiar with the story, the answer will come easily.
Dramatic conflict is created when a character is prevented from getting something he or she wants. Action is the result of conflict...Each character’s desire prevents the other [character in the conflict] from accomplishing his or her desire. The [story] is over when the conflict is resolved.
In John Updike's A&P, Sammy is at his job at the grocery story when three girls walk in wearing only bathing suits. It was very common at the time this story was written (and is still the case in some places today) that you weren't supposed to go into a public area (store or restaurant) without proper clothing. To the point, these three girls are breaking store policies (rules), and although they are in the "wrong," Sammy feels the need to step in.
Sammy is quite taken with one of the girls who carries herself 'like a queen.' Sammy describes how she looks and even how she moves when she walks up and down the aisles. He is a boy taken by the beauty and grace of a girl, and affected by his own naiveté and an age-old sense of honor.
As the girls approach the check-out lane where Sammy is now stationed, the store manager reproaches (scolds) the girls. This is where the dramatic conflict arises. The conflict here ends up being between Sammy and his manager. The manager wants the girls to conform in their dress—this is his desire; and Sammy wants the manager to leave the girls alone—this is Sammy's desire. The store manager prevents Sammy from getting what he wants, which is the manager's change of heart/some tolerance for the girls and their attire. Because Sammy cannot get his way (which the reader can see coming), his final act is to quit his job.
It is at this point that the dramatic conflict ends. The manager has no intention of backing down; Sammy's resignation does not change anything—the girls are long gone; and, Sammy is now out of a job. The conflict arises as Sammy steps up to defend the girls in what he sees as an injustice to them.