Could you go for the neutral approach like daily_deviant, and just use the blanket tag "content", rather than kinks or warnings? Because that way "content: noncon" could be a warning for, say, [Bad username: alisanne"] (picking on you cos I know you luvs the fluff :) ) and an enticement for me ;).
And then it'd just be a case of tagging significant *things*. But then, I still see people warn for m/m sex in slash! Gah, okay, I see your difficulty now - too much stuff to tag!
Hidden warnings-etc are good - I mean, I don't pick up a book in a shop and read the back to find out if anyone dies :).
For actual suggestions for content that could be considered negative - what Alisanne said looks like a good list, actually. Inclined to ask for chan to be divided up a bit more - some folk squick for under 18, some for under 16, some for even younger.
Sexual content - maybe? But unless the story is a PWP, is there much point tagging for, say, "fisting" but not tagging for "travel to Paris"?