I've never seen Mad Men, but your comparison seems at least a little unfair. In this case, knowledge of the particular meme or participation in the culture that created it is not necessary. A complete stranger to internet jokes, who happened to be at least generally acquainted with the technologies being discussed, could very easily identify Snowden's claim as a joke (or at least something very odd and worth investigating) whether or not they had been exposed to the original meme. "Seven proxies" should make your eyebrow raise whether or not you're aware of the original joke.
I've never seen Mad Men, but your comparison seems at least a little unfair..."Seven proxies" should make your eyebrow raise whether or not you're aware of the original joke.
Because, in your words, someone should know on the face of it, that "seven proxies" is implausible? Please explain how I should know that. Would it be worse or better if it were 6 or 8? Please answer from first principles concerning network technology. (The fact that you are not accounting for the fact that there are multiple interpretations to the term "proxy" makes my eyebrows raise.)
