I think it may actually be from _Think, Write, Speak: Uncollected Essays, Reviews, Interviews and Letters to the Editor_ instead. I spent an hour or so last night after seeing this tweet trying to track down the rest of this essay, and it took me a while to find the exact book it was from and find a copy of it. The funny part to me was that the whole essay was actually included in the tweets (aside from a footnote), it's very sort and pithy.