Toeing the line

My friend Leah and I are both working on YA novels and the question of so-called appropriateness -- where's the line drawn? -- almost always comes up. Is the cut off purely topical (ie: sex, drugs, rock and roll) or how graphic something is (ie: explicit sex, colorful drug use descriptions, Jonas Brother's concert versus Nordic black metal where somebody once filed a lawsuit over being concussed by a sheep head thrown from the stage)?