Alcohol and other intoxicants.

[quantumsaint]

There's a difference between imbibing a potion bottle that gives you various stat bonuses and penalties and labeling the bottle "Wine," and creating a system that turns you into a swaggering Drunken Master with the need to occasionally zip down your pants and vacate your bladder (such as in Age of Conan). The more level of detail you add, the more you glorify it, the more likely you'll earn a mature rating.

And frankly, this isn't a game that needs mature content of this nature. When did public drunkenness ever fit into the theme of Final Fantasy?

Pirates in Limsa Lominsa, Turks in VII, the pubs in Tactics...alcohol references in FFVI that were nixed by NoA...Jecht in FFX...there's numerous alcohol references throughout the series, and as I listed before, nearly every other MMO includes some form of intoxication. You may not want "mature content of this nature," but that doesn't mean others don't.