A fetish for calling each other 'man'

 I'd never looked into the origins of people calling each other "man" and assumed it was something ancient. Robin D.G. Kelley says in his biography of Thelonious Monk: "And in a world where whites commonly addressed them as 'boy,' young black males made a fetish of calling each other 'man.'" (Well, those things can both be true: that people have forever been calling each other 'man' but young blacks in the 1940's made a special thing of it.) He has a footnote for this which leads to three different cites.

Online etymological says it arose in Middle English but became "especially popular" in the early 20th century.