Google's AdSense description promises ads that are "relevant to your audience and your site content—ads so well-matched, in fact, that your readers will actually find them useful." (Sure, "protecting marriage" is a big concern of Pirate Cat listeners.) The ad is no longer showing up on Pirate Cat's site today, so apparently the "error" has been fixed.
Thanks to our commenters for the great info! Here's how to block unwanted ads, info via wchase via Scott Beale. Ggarrett notified us of a great discussion of this very circumstance. Someone within the aforementioned discussion sent a complaint to Google about these ads, and they were taken off the site within thirty minutes.
