Life Imitates Ad. Following up on this post, it seems like Coke Zero has gotten itself in a real trademark litigation. According to Law.com,

Last March, Baig's attorneys contacted Coke for the sixth time in a formal demand letter. On June 5, Coke received yet another letter from Baig's counsel stating that Baig was 'dead serious about filing suit' and promising to forward a copy of the complaint he intended to file if Coke did not meet Baig's demands by June 13. That complaint, according to the Coke pleading, never arrived.

I would say that that should be sufficient to support a DJ action.