"I know it when I see it." Excellent. Broad enough to cover every fart app ever conceived, specific enough for "we found it offensive and without redeeming qualities," and clear enough to remind submitters that Apple is in charge.
The most entertaining part is that they have specifically reminded submitters that "the more expensive your app, the more thoroughly we will review it." Also excellent. If you want to make a mint off of the platform, be prepared to defend it like a PhD dissertation.