Double post
Another thought. Being Brony might be why he doesn't want to identify with being a Republican. Republicans usually want to see young people taking up jobs, homes, families, and responsibilities and get involved in the "real world" pretty soon. Liking MLP would be ridiculous in the eyes of the average Republican, especially considering he is a man.
Democrats tend to be tolerant of this sort of thing (Along with everything else...) but he doesn't agree with them.
So Libertarian is really his only option unless he stops being one.