Since there always two, and one of them is usually good, there HAS to be an evil one.
Evil Twin. Could be a horse ranch in Tallahassee, or it could be the naughtier half of a split egg that likes to have fun, or it could be both of the twins. I have that shirt too.
Evil Twin, in dark devil red and black, complete with horns to really get the point across. This is the EVIL Twin of the two. Goes great with the Good Twin shirt as a joke between twins that we don't always get to share in.