The book's about a kind of hip speech that started off in the 1920s, born of an alliance of jazz musicians, white bohemians, and gangsters, thrown together by Prohibition. It drew on foreign languages- 'hepcat' and 'honky' are from the West African Wolof, 'drag' is a literal translation of the Yiddish 'schlep' - and playful, elaborate terms from crime and music - a 'Chicago piano' was a Tommy gun, while playing a non-metaphorical piano was 'battering the elephant's teeth'.
This lingo was popularised by musicians such as Cab Calloway, and, a bit later, comedians like Lord Buckley, who translated Mark Antony's oration over Caesar into hep-talk; 'Hipsters, Flipsters and Finger-Popping Daddies, Knock me your lobes...'. Crime novelists picked it up and added to it - Dashiell Hammett managed to slip a hidden subtext into 'The Maltese Falcon' by referring to Kasper Gutman's young companion Wilmer as a 'gunsel' - which sounds like another word for a gunman (which Wilmer also is) but actually, to those in the know, means a young boy kept by (and for) an older homosexual.
Decharne argues that hipster talk died out (as living slang) in the mid '60s, killed off by psychedelia, and the rift between black and white America that followed the death of Martin Luther King. Today, what's striking is the fact that it remained basically unchanged for so long.
Part of the point of slang is to act as a shibboleth, to mark out the in-crowd from everyone else, whether for reasons of race, youth, or just generalised hipness. Calloway could call a song 'Reefer Man' precisely because he knew that most radio programmers wouldn't have a clue what it meant, and wouldn't be able to find out.
Nowadays, of course, even white middle-aged academics like myself can stay down with da kidz, courtesy of websites such as www.urbandictionary.com. I'm not stupid enough to think that knowing what 'nang' means makes me, well, nang - my students probably regard that one as quite archaic. Nick Hornby has argued (in '31 Songs', p. 166) that one reason for the popularity of gangsta rap and death metal is the increasing difficulty for teenagers of finding a life-soundtrack that their parents won't appropriate, and I'd guess that a similar process is going on with slang, as terms become unfashionable at an ever greater rate. As Andy Warhol nearly said 'In the future, everybody will be hip for fifteen minutes.'