We say 'dirty sex' nowadays,quite often. When we're referring to hardcore sex that includes role play, bondage, sex toys and whatever else goes beyond the simple act of copulation, we say 'Dirty sex'. But when has this phrase first started to be used? Is it something people would say in North America at the beginning of the 20th century?
The earliest use in the New York Times is from 1972:
New York Times Movie Mailbag BRENDA H. HAWLEYDEC. 10, 1972 To THE EDITOR: In his selection of these film roles and what he selects to admire about them, Hirsch clearly reveals one of the bases of the Tuesday Weld cult. Tuesday has long been admired by fellers like him who see in her the embodiment of the exploitative child‐woman. The sex kitten who consumes and destroys. Tuesday of “the angelic face” who plays the dirty sex game. But now there is “Play It As It Lays” and that image is gone. . .
Another, in an article about farm communities (NYT Magazine), 1973:
Out in the Country By MARK KRAMER FEB. 17, 1973
The trouble is more manifest in the numbness of the thousands of victimized young people who grew up on farms and, having been turned away from that life by the economic and social conditions of our times, live Instead with TV, discount stores, and an ethos crackling with the mystique of dirty sex and violent punishment, daringly expensive playthings, and the universal veneer of middle‐class grace, unwittingly learned from the goodnatured and hollow folk who populate the world of TV.
These appear to be the more modern use.
The relevant context is " When you shall have learned, dear ladies, to keep your domains clean without so furiously getting them clean, you will have earned, in our eyes, your somewhat dubious title of housekeepers. Meanwhile, continue, in heaven's name, to think us the contentedly dirty sex!!" –
First I thought this to be an early mention of "dirty sex" so I checked for all other occurrences of sex in this text and realized all mentions of sex in this book imply the female sex, women. including the above quote.
to think us to be the contentedly dirty sex
So this is not really an example of the expression "dirty six" but an assertion about cleanliness!
Looking a bit further there are a few combinations of dirty + sex from 1914
A good way to discover when phrases were first used is to use Google Ngram, almost certainly they date from before then.
The first use of the phrase dirty sex, that I could find, was in 1908 or 1909 in the The American Magazine.
EDIT: I looked up dirty sex vs kinky sex too, the later dates to 1904 afaics.