I believe this is False Dawn by Chelsea Quinn Yarbro, published in 1978. I own only the German version (Falsche Dämmerung, Heyne 1980), so digging for quotes does not make much sense.
The following synopsis is from http://www.apocalypsebooks.com/books/false-dawn/. I put in boldface details that fit the question.
In a brutal and wasted world there was only one law—survive at any
It is the turn of the twenty-first century, War, disease, and
pollution have made the Earth nearly unfit for human habitation. In
America, food is scarce, and what food remains is quickly confiscated
by the Pirates—a murderous band of raiders determined to save
themselves and to destroy the last stronghold of civilized human
beings—the mutant population.
One of these mutants, a woman named Thea, has eluded the Pirates for
years. Armed only with a crossbow, her pride, and her common sense,
she has been slowly making her way Eastward to Gold Lake—a legendary
place of safety and enlightenment. Until one day she meets Evan
Montague, a man who needs her help, a man who is also on the run from
the Pirates, but for a different reason—he once led the Pirates
himself and has now become their most bitter and most hunted enemy.
Together, Thea and Evan trek across a dangerous and wasted California,
hoping to survive the brutality of twenty-first-century life... and,
perhaps, to find Eden before they die.
But what really makes me sure it is False Dawn is the part about the nipple. I clearly remember a scene where Thea (the main protagonist in my memory) puts up a fight, and her opponent says something like, "Stop it, or I will tear the other one off with my teeth."
Not for the faint of heart, but an impressive work that made me a Yarbro fan.
PS I have been lurking and reading for a while, but this is my first answer. Hints for improvement are most welcome.