As I have noted elsewhere, I don't have a lot of "guilty pleasures," because I try to own up to what I read and watch and enjoy. And because, in a way, being a fan of fantastika means that anything I read with that designation is thought of as a guilty pleasure by many "ordinary" folk (and sometimes, by connoseiurs of the fantastic as well). Which make me sad for them, sad that they feel they have to label anything not "mainstream" or validated by some hegemonic cultural agreement to be somehow innocent or upstanding as something to feel "guilty about." Certainly, the idea of guilt has a range of meanings, from severe judgment to joking, but the notion that we should feel in some form (even playfully) ashamed about our choices of art seems more about the reinforcement of rather stolid norms than about looking at our pleasure from different angles.
Generally, I would put some of my sword-and-sorcery reading and movie watching in this category. It's less a question of feeling apologetic than talking about pleasures that deviate from certain standards. I have read sword-and-sorcery since I was a teenager and despite some of its excesses I often find it more satisfying as pleasure reading than epic fantasy or urban fantasy. Why?
"While lurid and often emotionally stunted, there was a genuine pleasure to be had in the adventures of these flawed protagonists. Problems could not always be solved with wit or moral fiber; destiny and the favor of the gods could be a right pain in the ass. And the frequent delightful skewerings of upper classes and power structures appealed to me . . . .It is that distinctive combination of overflowing fecundity and bold indulgence in the pursuit of avaricious adventure with resistance to political, social, and cultural norms that has kept sword-and-sorcery appealing to me.
While these tendencies often arose in other fantasy subgenres, they were fully realized in S&S. Panache and excess were encouraged and could be used for tragic and comic effect by writers, made more intense by the often small-scale, personal stories being told. The visceral intimacies, the sensuality of all aspects of life, and the suddenness with which fortunes could change and lives could be lost were heady."
Fortunately, the requirement is for a "book," not a novel, so I will put forth the Flashing Swords anthologies, specifically the first volume, which is a collection of novelettes that give the reader a variety of approaches. In one book you get the sly fun of Leiber's Fafhrd and the Grey Mouser, the stylish decadence of Vance's Dying Earth, a great saga-like tale from Poul Anderson, and a brutal introduction to Amalric the Mangod by Lin Carter. It is a mixture that for me codifies the manifold pleasures of sword-and-sorcery, and also demonstrates some of the things that make me uncomfortable sometimes (such as the palpable testosterone in Carter's story). Flawed heroes in imperfect worlds try to survive and sometimes do a bit of good, challenging powers beyond their ken; the stories are rich, lunatic excursions into other worlds, quintessential S&S.