Tricking someone into sleeping with you is wrong but it isn't rape. I would agree there could be cases were it was true and the twin brother case would fall into that. I can imagine other cases as well such as slipping into a drunk women's bed and letting her believe you are her husband or boyfriend. If on the other hand I said I was the base player for Stiff Little Finger and some girls sleeps with me that isn't rape. It may be wrong but it isn't rape and it should not be considered a crime.