I remember that book! It was a hilarious introduction to "preppy style" for a girl growing up in the ranching country of the Northern Rockies. It inspired a local parody--An Official Guide to Stampede Wear. The local version included tips such as the following:
Never tuck your jeans into your cowboy boots
Never wear your cowboy hat tilted to the back of your head.
Only wear a large belt buckle if you won it at a rodeo--and, in that case, the larger the better!
A string bolero is the only tie ever worn with a yoked, western shirt.
Wranglers, not Levi's, are cowboy jeans.
For the record, those of us growing up in the western foothills could never envision any male actually wearing those pink trousers, even if the Guide insisted it was so.