When I teach entrapment law, a student sometimes asks if it's entrapment for a undercover cop to lie when asked if he is a police officer. Lots of people think it is. This comment about a prostitution bust is typical:

When will folks ever learn? Ask "The Question" before you do or say anything that can get you pinched for prostitution (giving or getting). What is "the Question"? Simply this... Ask the other person in the planned transaction "Are you a police officer or are you in any way working directly or indirectly with any law enforcement agency?" If they do anything but immediately answer "NO" get out of Dodge. If they are cops or are working with them they will try and avoid answering the question or will try some kind of weasel answer. If they are working with the cops in any way and lie and say "NO" then the entire 'crime' is entrapment and anything (evidence or testimony) gained is inadmissible in court. In some jurisdictions they have tried to criminalize asking "The Question" but there is no way to criminalize it without violating several constitutional rights so any such law, whenever challenged, quickly falls. Just more cases of only the uninformed or stupid getting caught. Ah well...

  Of course, that's not the law, at least in the United States. The commenter's understanding is hilariously wrong, and no doubt a lot of cops find it particularly amusing. But here's the question: Where did this rumor come from? Why do people think this is an accurate statement of the law? Does anyone know the source?

  I'm asking in part because I'm writing the entrapment materials for the new edition of Kamisar, Lafave, et. al., Modern Criminal Procedure. My thought is that if a lot of students have heard this rumor and there's a good story behind it, it might be worth pointing out the history of the rumor (and that it's wrong) in a note. Oh, and I have a vague feeling that I might have posted on this topic at some point years ago. If I have, I apologize for the repeat; I looked in the archives and couldn't find anything.