At risk of repeating myself, the clown euphemisms are completely useless, self-defeating (as they are almost invariably accompanied by descriptive context that tells the person exactly what the euphemism means), and hypocritical coming from anyone who espouses concealing spoilers.
If protecting the poor innocent newbies from the evil spoilers (such as they are) is that important, you can choose not to mention the demons at all. I personally am not likely to bring them up at all, except where it's relevant. But I will have absolutely nothing to do with this "clown" and "cotton candy" crap.
Spoilers aren't about gameplay, they're not a "oh hehe, we are so clever to screw people over" kind of thing. The reason it's there is because there are people who don't want things spoiled, and we should give them the tools to stay unspoiled.
They
are about gameplay in this case, because Dwarf Fortress has nothing
but gameplay to be spoiled. Demons and Hell are gameplay mechanics, just like farming, combat, nobles, and sieges. And players who are inadequately prepared for
any of the above, through ignorance or incompetence, will lose their fortress all the same (
well, maybe not from nobles, but then their shenanigans can get pretty spectacular). Given that all of the above will mess a player up if they don't know about it, what makes demons so special?
If a player so wishes to avoid being spoiled, the solution is as simple here as with any work -
stay off the damn internet. Because even browsing the wiki, universally toted as the single most useful resource a new player can ask for, can inadvertently expose players to the features deep below the earth, entirely by accident.
As an example of how simple this is, we'll take the article of one of the most fundamental buildings in the game: The
furnace, which contains a link to
Magma, which contains a link to
Semi-molten rock, which contains a link to
Hidden Fun Stuff (also known as
Hell). Just three clicks is all it takes, and that spoiler tag isn't going to make the player forget that it's there, even if it does convince them to look the other way.