If you accept it's necessary - and you're the unlucky slob who has to enforce the rule - you have to go to extraordinary lengths to do so. When I last mentioned it, it was in the context of a filter to stop the public writing offensive tags on a library cataloguing program. The wider argument was about what is offensive, which turned out to be a surprising variety of things. In fact, it would be easier to give a list of non-offensive words that could be used to catalogue books than to try to keep up with some people's ability to find offence.
Comments like this were bandied about:
If there are issues with the word testicle, then perhaps scrotum and ball-sack might be considered? My son, who is 'In the Army Now', would definitely use those instead of testicle(s) although he probably wouldn't spell them correctly.
And then we got into whether "leet" (1337) variations of the same might profitably be banned. And whether, say, a book about testicular cancer could be tagged with the word "testicle", on the grounds that some, e.g. sufferers from testicular cancer, might find it useful in a way that trumped someone else's right to be offended.
And there was much more to it. (Original post on Making Light is here.)
Today, the Supreme Court has been faced with a similar task, to decide whether "fleeting expletives" in broadcasts should be punished by the current penalty (hanging, drawing and quartering) or whether broadcasters should simply be forced to crawl on their hands and knees all across America and apologize to every child they harmed.
The Supremes took a completely different tack. Expletives, fleeting or lingering, apparently fall foul of a law prohibiting material that "depicts or describes sexual or excretory activities or organs". And that's it!
The New York Times reports:
“Why do you think the F-word has shocking value or emphasis or force?” Chief Justice Roberts asked Carter G. Phillips, a lawyer for Fox Television Stations, which had broadcast some of the offending language.
The chief justice answered his own question: “Because it is associated with sexual or excretory activity. That’s what gives it its force.”
Justice Antonin Scalia added that this was the reason people “don’t use ‘gollywaddles’ instead of the F-word.”
There's quite a lot more at the link - the discussion of a possible "but it was funny!" defense, and the offhand declaration that "dung" seems to be acceptable but "shit" isn't. Not that they said "shit". The solicitor general said, "We think that the S-word is patently offensive".
I'm still not sure how to reliably differentiate between a person who describes excretory activity because they have a mandate to educate, and someone who says, "Shit! Tee hee! I made a funny!" but I guess they know, because one is an expletive and one isn't.
I suppose I'll know it when I see it.
 "Fleeting Expletives" would be a good name for a band!