"bitchin" is an idiomatic expression originally from the left coast of the United States of America, circa mid to late 1970s, coinciding with the rise of Disco(the Bee Gees), and the "
BITCH" fashion trend (where young "woman'
s libbers" commonly wore necklaces and shirts emblazoned with "
BITCH"), used originally by "surfer types", deriving from "man that wave is a
bitch" to "what a ride, that wave was bitchin'". It quickly spread to main stream American vernacular as an affermation.