For the last 7 or 8 years my sister, Natalie, and I have called each other "Mavis". We aren't really sure how this started....maybe from a movie line "Beautifully done, Mavis" or maybe from "Mavis Beacon Teaches Typing"...no one really knows.
You may think this is confusing, not so. I call her Mavis and she calls me Mavis, easy peasy. Ethan, her son, calls me Aunt Mavis (closer to Aunt Mabis).
I love my Mavis! She is the best sister I have.