We used to kick around the following example. Suppose you have Jewish friends over for dinner. A knock on the door reveals a German gestapo agent, looking for Jewish people. He asks, "Do you have any Jewish people here?" Do you tell the truth or do you lie?
The answer to the question, and the rationale for lying can be understood if we frame the question differently. Suppose he asked, "Will you help me kill the Jews by telling me where they are?" The obvious answer is "No, I do not wish to help you and participate in genocide." In this way, we understand that often times there is a hidden question behind a question and in order to tell the truth with regard to the hidden question, we are sometimes force to lie with regard to the explicit question. By saying, "No, there are no Jews living in this house," (which is false) I am also saying, "No, I do not want to help you commit genocide." (which is true.)
If a woman asks her husband, while he is watching TV, "does this dress make me look fat?" What is the hidden question? It might be, "are you willing to stop what you are doing in order to notice me?"
Maybe.