When I was a boy, a boob was simpleton, a nimcompoop, what Shakespeare calls a mooncalf and what in an earlier life I might have called a schmuck or a schmendrick. "Boobs" was an everyday expression; so common and pervasive that The Three Stooges might just as easily have been called the The Three Boobs. There were other related uses of the word; "booby hatch" -- a semi-humorous appellation for what used to be called an insane asylum, and also the "boob-tube"-- though whether the boob in that doublet denoted the machine itself or the or the schmendricks who stare at it was never clear to me. But at some point in my linguistic career the word "boob" re-emerged with a new primary signification. It now seems to have become the most common word for the female breast.
I do not like it when a breast is called a boob. It is disrespectful. A breast is soft and nurturing but also erotic and enticing. A boob is neither; it is a denatured object, stripped of its warm associations and joined instead to foolishness and boobery. "Boob" is a deliberately unsexual and undignified term. It is also, as Shakespeare says in a different context, "base, vulgar and popular."
And available. If a person should happen to google the word "boob," perhaps searching for information of an etymological kind, the first, second, third and perhaps hundredth entries that he or she will encounter are for "boob selfies." A "boob selfie," for readers equally as naïve as me, is a photograph which a woman takes of her boobs and posts on the internet. Jane Austen did not do this. Neither did George Eliot. I can't demonstrate that the word "boob' is responsible for such a decadent display of immodesty, but I do note that "breast selfies" or "bosom selfies" are both inconceivable.
Nor did suicidal Cleopatra say, when bringing the venomous asp to her breast, say "Peace, peace/ Dost thou not see my baby at my boob/ That sucks the nurse asleep."