Nudity

I'd like to propose that the rule about not posting nudity should be updated to specify what exactly constitutes "nudity". What parts of the body cannot be displayed? Can a photo be in violation even if none of those parts are on display?

For instance, suppose someone posts a pic where they are clearly not wearing any clothing but show no parts of the body that couldn't be displayed in, say, a Sports Illustrated magazine that you could buy in a Walmart. Is that nudity? Maybe so, maybe not - but without a clear definition of the term in the guideline, it is left up to the subjective opinion of each moderator. I'm sure the moderators are doing their best, but everyone operating on an "I know it when I see it" basis as appears to be the case now doesn't seem to lead to the most consistent application of the rule.