Originally posted by Nuns:
Never end a sentence in a preposition. The second run nets -3 yards. Think before you embarass yourself.
FYI, that's not correct. He messed up because he ended his sentence with an unnecessary, extraneous preposition. That is, if you take "at" out of his sentence, his sentence makes perfect sense.
But there's nothing wrong with ending a sentence with a preposition when that preposition is necessary. What are you looking at? (At what are you looking?) What did you step on? (On what did you step?) The list goes on.