n. The practice of one person trying to do better than or to prove themselves superior to another person.
In the book world, we're proclaiming sunshine (at least when it's not pouring) and the open air; we're discussing Tent City, conviviality, occasional verbal punchups, the excitement of ideas, a crush of communality and highlevel one-uppersonship, all awash in a sea of South Australian wines.
—Murray Waldren, “All roads lead to Adelaide,” The Weekend Australian, February 28, 1998
1994 (earliest)
And talking of bankers, what did the best-dressed guests at the official opening of a new bank in Singapore last year wear to the occasion? One trusts they did not take the dress-code indicated in the invitation literally. Dress: Lounge suite, it advised. No doubt the opportunity for one-uppersonship immediately presented itself to the purely vain and fashion-conscious with a full wardrobe of furniture who decided to eschew the two-piece for the more formal three-piece (settee and two chairs).
—Louis Beckerling, “1993: The Year of the Stag,” The Straits Times, January 02, 1994
This word is the gender neutral version of one-upmanship (1952) and the earlier Word Spy entry one-upwomanship (1977).

The earliest citation I could find was the single-word heading "One-uppersonship" over a letter to the editor in the October 8, 1988 edition of The Globe and Mail.
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