There's already making of gristly trophies by invading armies. Not any rape or sexcrimes outside night trolls and that one story...
I wasn't thinking of rape when I asked the question but instead things like leaders being influenced by a beautiful villain. Also situations like the one in Beowulf.
Toady said that he wasn't morally opposed to the depiction of sex, though he was opposed to explicit depiction of rape and other sex crimes. However, he was wary of the media attention it would bring. The stuff you suggest is probably planned, but won't be implemented for quite a while.
Many of the reports that come through announcements, combat, sparring, and hunting logs would earn the game an 18+ rating, if it were not ASCII. The latest set of updates I've put through to the Masterwork succession fortress are highly indicative - continuous rioting, disorderly conduct, vandalism, dehydration, major dysfunction of the legal system, blood-sucking mayors, dwarves forced to drink vomit, dwarves stripping off, going berserk in hospitals, slicing unicorns in half, sieges, rains of beer, massive junk stockpiles...
While I was uploading the files to the website, I actually tried to find a way to mark the ASCII screenshots as "18+ (Violence)", but couldn't find an option to do so.
Toady has said in some other thread on old projects of his that he doesn't want to release certain things that are very politically incorrect. We've already had the removal of certain "naughty words" (many of which are not even "naughty" but just cover politically taboo subjects) with the DF2012 release, although the dictionary was expanded considerably in other ways, so he does find it an issue even if many players don't. I do think the game will need to go someway there when the relationships system gets worked on, and this might even be the next release or so (after DF2013).