While I understand the idea behind "Christians Against Christians", I think it may be the wrong kind of approach for a t-shirt/slogan/label/whatever.

Just as Democrats couldn't win in 2004 by just being against Bush, I think it's so much more powerful and productive to define yourself by inclusion and supporting what you <i>do</i> believe in rather than by what you <i>don't</i> agree with.  I guess that's why I've mostly identified as <a href="http://en.wikipedia.org/wiki/Unitarian_Universalism" rel="nofollow">UU</a>.