Why does the Pasuk repeat "the men of the town, the men of S'dom"?
Rashi #1 (citing the Midrash): Before they retired, the guests questioned Lot about the town's inhabitants, to which he replied that most of them were Resha'im. They were still discussing the subject, when (as if to prove Lot's testimony) they appeared in person.
Rashi #2: 'The men of the town - who, due to their wickedness, were dubbed - 'the men of S'dom'. 1
Rashi #3 (On Bereishis Rabah): 'Anshei ha'Ir" refers to people who had come to live in S'dom from other locations; "Anshei S'dom", to the natives of S'dom.
Why does the Torah see fit to stress that the entire town came looking for Lot's guests?
Rashi and Rashbam: To demonstrate that there was not a single Tzadik (let olone the ten requested by Avraham) in the entire town To stop them.