This afternoon we received an e-mail from a Facebook spokesperson who revealed:
"This error isn't specific to any one account. It's generated when a person has been blocked a certain large number of times. In very rare instances, a viral campaign will develop instructing lots of people to all wrongly block the same person. The purpose of this system is to protect the experience for people targeted by these campaigns. We're constantly working to improve our systems and are taking a closer look at this one."
It's not as fun an explanation as CEO vanity or developer facetiousness, but there you have it.
Attention to Zuckerberg's unblockable status was initially brought by the website Block Zuck, but Gawker spoke with the website's founder and learned that the site was originally the base of operations for a viral campaign to mass-block Zuckerberg in protest of the social network's controversial user privacy policies.