Karlach's language alone would be enough to get this an adult rating!

(For the record, I'm no prude, I've enjoyed all the grown-up stuff, and think on the whole they've done a good job of using it proportionately and non-gratuitously. The only bits that made me wince a bit were the pointless gore of the various arms, legs, intestines and heads dotted around the landscape. If I can't build my own girlfriend out of them or feed them to a gnoll for a favour, why are they even there?)