What would be a good thesis statement along the lines of Sammy being a little gross in claiming those girls in John Updike's A&P? It really hit me when my teacher pointed out towards the end of the story Sammy claims the girls as "his." Re-reading all the descriptions with that sense of possession in mind makes the whole story feel really dirty to me and I'd like to focus on that but can't seem to find the proper words.
In Updike's story, set in first person perspective, the main character/narrator is an adolescent on the cusp of manhood who is exploring various potential facets of his identity: as a worker, as a man, as a lover, as a provider. The era during which the story is set portrays a male-dominated culture that has only begun to consider equal rights for women, and the concept of female sexuality is still fraught with sexist notions of the frail feminine or women being limited by cultural expectations.
When these girls, who are dressed provocatively, enter into Sammy's world, they catalyze his internal conflicts over his identity as a sexual male and as a male in general. When his boss speaks rudely to the girls, chastising them about their revealing clothing, Sammy,having already been frustrated by his experience working at the A & P, decides to make a show of courage and dominant behavior by loudly announcing "I quit" for the girls' benefit.
Despite the fact that the girls don't pay much attention to him, Sammy's behavior indicates he feels qualified to be their protector, and his physical attraction to the ringleader of the group (who is wearing the most suggestive clothing) causes him to try and behave with chivalry. But to our modern sensibilities, his protective attitude feels sexist and inappropriate.
RE: "... Sammy being a little gross in claiming those girls in John Updike's A&P"
A thesis statement answers a question that is important to you, and that you also predict is important to your readers. So the place to begin constructing a thesis statement is with a question.
Your initial thoughts about "Sammy being a little gross...is too general and vague. Readers will differ on what "gross" means as well as a "little gross." The same goes "dirty." How else could you characterize Sammy's attitude? Appletrees' last lines are a good place to start.