For reasons of my own, I looked up the etymology of boob. It seems to have come from booby (so not the other way around, we dropped off the y instead of adding it). Booby seems to have first meant fool, and then meant that silly bird, and only then, after both of those, meant bosom.
The kicker? Booby seems to have come from pooby. Pooby! Per the Random House Dictionary, pooby was coined between 1590 and 1600, as a blend of the words poop, befool, and baby. Pooby.