What an odd thing to plagiarize! Why on earth would anyone want to take your by-line - as that describes who you are!
1. You could ask them to remove it and come from a humorous angel - not realizing you had a twin... You could tell them they have unique qualities that make they who they are and to use those in their by-line. Plus you could say you realize that they may be new to the web and may not realize that you're not to copy another person's work without permission.
(I don't think this type of copying would fall under the fair use part of the copyright act in the US or fair dealing in Canada.)
2. If that doesn't work - then report it to the webhost/service. Let them know that you've contacted the person on x date and asked them to remove it and they did not.
3. Do what a friend did when there was a double-booking for an event space. Imagine the issue resolving exactly as you want it to. See it in your mind. Feel how you'd feel if it was solved.
Hope that helps.