A Texan was visiting Harvard University, and was lost. He stopped a student and asked, "Do you know where the library is at?"
"I sure do," replied the student, "But, you know, you're not supposed to end sentences with prepositions."
"What?"
"Prepositions. You ended your sentence with an 'at', which you aren't supposed to do."
"Oh, ok," said the Texan, "Do you know where the library is at, a$$hole?"