I mis-remembered the joke. Here it is:
A Texan is visiting a friend at Harvard, and they agree to meet at the library. He's a bit lost, so he stops a passing student. Texan: "'Scuse me, could you tell me where the library's at?" Student: "Around here, we don't end our sentences with prepositions." Texan: "All right, could you tell me where the library's at, asshole?"