The classification is really a bit fuzzy, but not really that much: many pools are automatically disqualified unlike the non_violent tag, to begin with; shitheadness can really be defined only in context, for example with surrounding text (and here comes the "lack of translation" issue that is also present with the family_friendly tag), so many one-shot illustrations can be tagged safely as there are not enough informations to define a yukkuri a shithead or not; lastly, I personally don't see anything wrong in opening a forum thread (or posting a comment) to discuss wether a picture falls in the category or not. What I mean is that people shouldn't be afraid to ask before tagging, if they have doubts about a particular tag.