1925, U.S. slang, "sexually provocative;" later (1930s) "spiteful, catty, bad-tempered" (usually of females); from bitch + -y (2). Earlier in reference to male dogs thought to look less rough or coarse than usual.
Mr. Ramsay says we would now call the old dogs "bitchy" in face. That is because the Englishmen have gone in for the wrong sort of forefaces in their dogs, beginning with the days when Meersbrook Bristles and his type swept the judges off their feet and whiskers and an exaggerated face were called for in other varieties of terriers besides the wire haired fox. [James Watson, "The Dog Book," New York, 1906]
Related: Bitchily; bitchiness.