There was a sci-fi book a while back where all humans were gone, and all that was left was a thriving android civilization expanding across the solar system. The main character was built on the base of a sex bot, and had the ability to set the speed of her hair growth, and color. At one point she gets tied to some tracks (a city on Mercury that traveled around the planet) to be eliminated (she was a spy) and ends up getting away by forcing her hair to grow at a rate so fast it came out weak and easy to tear. Super weird book, but I thought of it when I read the comment I was responding to. And yes, on/off was part of it.