So Au-ra females are not supposed to have boobs? What's wrong with Au-ra females having boobs? What should they have instead? Breasts?
Yeah I know its not a good pun. Historically boob comes from bobos which means stupid, idiot or fool. Hence why that bird was named Booby (they were easily caught eaten by sailors). In terms of anatomy slang, its because of how some/most men/males act or react to their presence. Either becoming temporarily stupid, easily distracted, or just briefly detached to reality by what is being said to or happening around that person due to the shift in focus. In this sense its more of a cause of mild stupidity than the result of. As for breast, both men and women have them, they just develop differently.