Most pop songs are sincere confessions of love sought, lost or acquired. Yet every decade seems to spawn one or two humorous novelty blockbusters. A nascent radio star in 1947, Arthur Godfrey scored big with “Too Fat Polka.” In 1969 Ray Stevens spun a jaunty, guitar-playing King of the Jungle into “Gitarzan” gold. When “The Treasures of Tutankhamun” exhibition toured the world, Steve Martin cashed in with “King Tut,” which he performed in 1978 on “Saturday Night Live” in culturally appropriating faux-Egyptian regalia.

Rarer...

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Most pop songs are sincere confessions of love sought, lost or acquired. Yet every decade seems to spawn one or two humorous novelty blockbusters. A nascent radio star in 1947, Arthur Godfrey scored big with “Too Fat Polka.” In 1969 Ray Stevens spun a jaunty, guitar-playing King of the Jungle into “Gitarzan” gold. When “The Treasures of Tutankhamun” exhibition toured the world, Steve Martin cashed in with “King Tut,” which he performed in 1978 on “Saturday Night Live” in culturally appropriating faux-Egyptian regalia.

Rarer still is the political novelty song. Harvard mathematician Tom Lehrer penned sardonic Cold War admonitions—“So Long, Mom (I’m Off to Drop the Bomb)” and “We Will All Go Together When We Go.” And one such hit, 101 years ago, proved to have staying power.

Gus Kahn’s name isn’t as recognizable as Irving Berlin, Cole Porter or Ira Gershwin, yet during the Roaring ’20s and the 1930s this German-born lyricist gave America many treasured love ballads, among them “It Had to Be You,” “Love Me or Leave Me” and “Dream a Little Dream of Me.”

A tune he wrote in 1920 won instant popularity for its droll attitude toward the hard times America faced as it struggled to reabsorb millions of World War I veterans into the workforce. “Ain’t We Got Fun?” premiered in the musical revue “Satires of 1920.” The music was composed by Richard A. Whiting, the lyric co-written by Kahn and Raymond B. Egan.

Nowadays the crash of 1929 gets all the attention, but during the Depression of 1920-21, the stock market suffered a serious break, worse than the 1907 panic. The subsequent bear market lasted 22 months. By August 1921, when the Dow Jones Industrial Average hit bottom, it was down 47% from its October 1919 peak. Countless Americans, many trading on margin, were financially destroyed.

The Kahn-Egan-Whiting song made light of the crisis. Its chorus relays the happy household chatter of a young couple married one year: “Every morning, every evening, ain’t we got fun? / Not much money, oh but honey, ain’t we got fun? / The rent’s unpaid, dear. We haven’t a bus. / But smiles were made, dear, for people like us.” The unhappy realization that “there’s nothing surer, the rich get rich and the poor get poorer” is shrugged off with the persistent ironic mantra: “In the meantime, in between time, ain’t we got fun?”

The droll ditty proved durable. “Ain’t We Got Fun” was recorded by Peggy Lee, Doris Day, Rosemary Clooney, even Mickey and Minnie Mouse in a 1931 cartoon. And the message is timeless. A century later, as we face income inequality, concentrated wealth and the challenges of globalization, we still got fun.

Mr. Opelka is a musical-theater composer-lyricist.

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