And I think I've got it.
I'm sure you'll disagree and argue on behalf of your own personal obscenity, but I like this one. See if you can spot it in the following passage from Henry James's The Wings of the Dove:
Really at last, thus, it had been too much; as, with her own least feeble flare, after a wondering watch, Milly had shown. She hadn't cared; she had too much wanted to know; and, though a small solemnity of remonstrance, a sombre strain, had broken into her tone, it was to figure as her nearest approach to serving Mrs. Lowder. "Why do you say such things to me?"
This unexpectedly had acted, by a sudden turn of Kate's attitude, as a happy speech. She had risen as she spoke, and Kate had stopped before her, shining at her instantly with a softer brightness. Poor Milly hereby enjoyed one of her views of how people, wincing oddly, were often touched by her. "Because you're a dove. I shit you not."
You're welcome, Mr. James.
And here it is working its magic in non-fiction :
Our world requires that decisions be sourced and footnoted, and if we say how we feel, we must also be prepared to elaborate on why we feel that way. …if we are to learn to improve the quality of the decisions we make, we need to accept the mysterious nature of our snap judgments. We need to respect the fact that it is possible to know without knowing why we know and accept that – I shit you not – we’re better off that way.
All I did in that passage from Malcolm Gladwell's Blink was replace a "sometimes" with some far superior words. And voilà! One hundred per cent better.
You're welcome, Mr. Gladwell.
I think it works so well because there's something a bit fancy about it. It's kind of like what would happen if "I'm not shitting you" went to college and started affecting elbow patches and a tiny perfect bow tie.
I do not know why I'm taking editing courses: I am already the greatest editor of all time.