Locker rooms have been with us since the middle of the 19th century, when they referred simply to rooms which had lockers and in which people changed their clothes. However, the word has also been used, for a considerable length of time, as an adjective, denoting things (especially talk) of a coarse or offensive nature.
Trump repeated his apology but downplayed the seriousness of his comments. "This was locker-room talk," he said.
-Chris Megerian, Los Angeles Times, 9 Oct. 2016
The adjectival use of locker-room has been combined with talk since at least 1921:
In the July issue of the magazine Mr. Richards has two articles: one on the Bloomfield Hills Country Club, in which he sketches accurately and in a delightfully humorous way some of the locker-room talk that may be heard at any country club.
-Democrat and Chronicle (Rochester, NY), 4 Sept.1921
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