I can't read a reference to "smutty books" without hearing the phrase as uttered by Hermione Gingold complaining about "Rubáiyát of Omar Khayyám," in the movie version of Meredith Willson's "The Music Man."
Marian Paroo: "It's beautiful Persian poetry."
Eulalie MacKecknie Shinn: "It's a smutty book."
"That's right. Some of the characters from Maas' best-selling series A Court of Thorns and Roses are starting to pop up on baby names lists in the U.S. and Canada."
https://www.cbc.ca/news/canada/a-court-of-thorns-and-roses-baby-names-1.7232325