Prepositions And Other Body Parts

In his review of David Crystal's How Language Works, John Humphrys narrates a grammatical anecdote:

...I applaud the rather gauche young man from the Deep South who, I was told when I was writing my book, won a scholarship to Harvard. On his first day there he approached a couple of elegant young New Englanders who clearly knew their way around. “Hey y’all. Can you tell me where the library’s at?” One of them looked down at him with disdain and sneered: “At Harvard, we tend not to end sentences with prepositions.” The young man thought for a moment. “OK,” he said. “Can you tell me where the library’s at . . . asshole?”