Robot tattoos are awesome. You could either get an old school, 1950's looking robot, or something more modern. They can be very cartoon like, or very realistic. There are so many ideas out there for robot tattoos. Just be sure to get a custom one drawn up by a solid tattoo artist.
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.