There will always be a gray area where it's not clear whether the language is "appropriate". I personally believe that we shouldn't be too squeamish when we are educating, and that using euphemisms can turn a good answer into something really hard to understand.
If you think someone is using profanity gratuitously, flag it and it will get looked at. I believe that the best way to handle things like this is old-fashioned human judgement. If you know of a commonly used phrase or word that isn't polite, but helps answer the question at hand, I think it is a good thing to include it with an explanation of when it might or might not be appropriate to use it.
If you don't want to answer questions about profanity or feel uncomfortable including profanity in your answer, that's perfectly OK. Just keep in mind though what might come up when a learner tries to search for an answer to an English question that has profanity in it.
Will looking for an answer to a question like the rude quote from South Park turn up an explanation or just more profanity-laden text? Wouldn't it be better if a search turned up the answer to that question because it had the actual "bad" words in it instead of "f-word" and "a**-spelunker"?
As a side note, the use of the spoiler tag in the question is a good technique if you are worried about upsetting people. Just mark the text with
Also, be sure to explain why you have hidden the text so curious people don't get a nasty surprise.
The text in the spoiler is still indexed by search engines, it's just rendered in a special way on SE sites.