this is the crucial reason why chinese eat dogs
ancient chinese culture think dogs is cheap, lowly because ancient china is agricultural country. not the price, i mean the value.
look at those stray dog. thin, illness, drooly, dirty, disgusting, sickness. they just know how to Ingratiate human, and do not have self-esteem. they are 贱的 like the position of bitch but without the licentious meaning.
so 狗男女 means those couple without morality（especially chinese morality-三纲五常、礼教）
there are so many 成语 having story behind. you can try to search in website to know.