Regardless of the n or r title, maybe the thing to do is to avoid using the words 'mature' and 'adult' as a descriptor for the folder because these terms are so open-ended, and also carry with them the implication that any story not in this particular folder is therefore immature and childish.
Instead the folder could state that it contains stories with explicit/graphic depictions of sex and/or violence, or those with coarse language.
C.
