Rubber Dicked

Originally a military slang term to indicate when a superior starts an apparently friendly conversation only to assign some crappy job duty to you. It has expanded in general use to indicate anytime someone is nice to with the sole intention of screwing you over. It is particularly appropriate for describing when someone is the victim of a "long con" or when you get burned so dramatically that it leaves no doubt that the person who did it thoroughly planned to do so. It comes from the idea of a husband who can't (or won't) have sex with his wife turning out the lights and screwing her with a rubber dick in the dark.