In "A&P" by John Updike, Sammy can be described as both narcissistic and hypocritical. His attitude towards others in the store is negative - and in the case of the three young girls, rather creepy. Additionally, he appears to think highly of himself, despite the fact that it is his duty to serve those he deems inferior. This characterization makes it hard to sympathize with his realization at the end of the story of "how hard the world [is] going to be to [him] hereafter."
Sammy's problematic attitude becomes evident at the very beginning of the story when he becomes distracted by the three young girls:
"I stood there with my hand on a box of HiHo crackers trying to remember if I rang it up or not. I ring it up again and the customer starts giving me hell. She's one of these cash-register-watchers, a witch about fifty with rouge on her cheekbones and no eyebrows, and I know it made her day to trip me up."
Despite being responsible for the mistake, he transfers blame to the woman by suggesting she was the one who 'tripped' him up. His description of her showcases his lack of respect for his elders, and when combined with his account of what the girls are wearing, it becomes clear that he places high value on external beauty.
A short while later, Sammy makes fun of the other shoppers, referring to them as "sheep" while commenting on how their reactions to the three young girls. The hypocrisy here is that in his own words, the patrons of the store pay relatively little attention to them, while he spends the whole time following them around the store with his eyes. In addition to this hypocritical nature of his behavior, it is also very creepy:
"She didn't look around, not this queen, she just walked straight on slowly, on these long white prima-donna legs. She came down a little hard on her heels, as if she didn't walk in her bare feet that much, putting down her heels and then letting the weight move along to her toes as if she was testing the floor with every step, putting a little deliberate extra action into it."
This passage - when added to his constant focus on the girls' bathing suits - makes Sammy come across as perverted at best. Though he is only nineteen years old, the reader gets the impression that these girls are a few years younger than him. This is where most of the creepy-vibe comes from, especially considering the way he keeps tabs on where they are in the store. Despite his own obsession, in his eyes it is the other patrons in the store who deserve to be mocked.
Another aspect of Sammy's hypocrisy has to do with his job as cashier. As previously stated, he refers to them as mindless sheep following the herd from aisle to aisle. However, what he does not mention is the monotony of his own job; one could argue that his task of scanning product after product makes him a sheep. In Sammy's mind, though, they are beneath him.
One final example of Sammy's character - specifically, his narcissism - becomes very clear during his attempt to impress the three young girls:
"The girls, and who'd blame them, are in a hurry to get out, so I say 'I quit' to Lengel enough for them to hear, hoping they'll stop and watch me, their unsuspected hero. They keep right on going, into the electric eye; the door flies open and they flicker across the lot to their car, Queenie and Plaid and Big Tall Goony-Goony (not that as raw material she was so bad), leaving me with Lengel and a kink in his eyebrow."
In reality, this act of publicly declaring "I quit" has relatively little to do with the girls themselves. Rather, Sammy does this to feed his own ego and make himself look better. As one would expect, this ill-conceived plan immediately fails; instead of becoming the girls' hero, he simply becomes unemployed.