As anyone who's ever drafted a public indecency law has surely learned, delineating which patches of skin should be considered "indecent" (when neighboring patches less than an inch adjacent may be deemed perfectly acceptable for public exposure) is an exercise in arbitrariness. That's why these things often focus on landmarks like nipples/areolas, pubic hair, and the genitals themselves (e.g., penis, scrotum, labia, anus). After all, how should one measure the curvature of a breast, or a pair of buttocks?
[description: portrait of a hairless nude torso, with hand covering the genital area]
As it is, though, removing one's pubic hair limits the amount of real estate that must absolutely be covered, giving you some measure of leeway - who's to say if that particular patch of skin lies within the "pubic area" if it is just as hairless as any other? The imagination thrills at the possibilities!
