Hey Mabel effect
n. Feelings of surprise, shock, and delight caused by certain situations, scenes, or news.
Examples
1999
With hundreds of carnivalesque pages, these catalogues score high on what television programmers term the 'Hey Mabel' effect—'Hey Mabel, you can use Liquid-Plumr and Tylenol to build a bomb!'
—Albert Mobilio, “The Criminal Within,” Harper's Magazine, March 01, 1999
1993 (earliest)
One of Mr. Dunn's early ideas resulted in "The Strippers," the newspaper's front-page article on a Sunday last month. The News had bought a 1985 Honda, parked it on a New York City street, and had its photographers watch. By the fourth day of the vigil, car strippers had reduced it to a bucket of bolts that was a "curbside blight and barely resembling a vehicle."

That, Mr. Dunn said, was the kind of "hey, Mabel" article (as in "Hey, Mabel, look at this!") that The News must present.
—William Glaberson, “Daily News Is Turning a Gamble Into a Rebirth,” The New York Times, November 01, 1993
Notes
The phrase "Hey Mabel" is most often used as an adjective — for example, a Hey Mabel story — where it describes something sensational or controversial that people will want to point out to others. (A variation is Hey Martha.)
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