A unicorn makes a beautiful tattoo. Some people get realistic looking ones, some people get cartoon style. Either way there are many ideas you could roll with. They look best in color in my opinion.
It is also a tattoo that can go anywhere on the body depending on how big you want it.
Many people love the Christmas season so much that they get tattoos inspired by the holiday. I have seen everything from Santa, snow, The Grinch and more. Men and woman have gotten these awesome tattoos. Just try and be original. Get a good artist to do it.