These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
"Book/Comic Conan" vs. "Movie Conan". Or rather fans of the latter who use it as their baseline for everything Conan vs. those who are at least aware of the stories. The Shallow Parodies more about Arnold than Conan don't help.
Constantius the Falcon and his queen Salome of the story A Witch Shall Be Born. Taramis herself is innately monstrous due to an ancient curse on her family, and she hand-picks Constantius to be her consort for his "utter lack of characteristics men call good." After Salome frees Constantius from the dungeons, the two quickly replace Taramis, with Constantius raping and brutalizing the queen for his amusement. Salome's only response is to gleefully tell Constantius to "tame her as he will." Under the ruling hand of the duo, Taramis's kingdom becomes depraved and dissolute. Constantius's soldiers abuse and violate the people at will with any who resist facing death or slavery. When Conan declares this 'Taramis' an impostor, Constantius captures him and crucifies him in the desert, leaving him to die of pain, thirst and the attacks of the vultures. Salome takes every chance to abuse her captive sister, presenting her with the head of her faithful friend and councilor, and allowing the guards to violate her multiple times. Salome also has a pet demon that she feeds humans to: when things start to go sour, her response is to loose the demon on the populace.
Valerius from The Hour of the Dragon. After usurping Conan's throne via the help of an evil wizard, Valerius realizes that once his allies have no more use for him, he'll be disposed of and replaced by a different king. So he decides to ruin the kingdom out of spite. He heavily taxes his subjects, and those who cannot pay are sold into slavery. He allows his soldiers to brutalize the common people and spends all of the kingdom's money on debauchery. He also sentences the Countess Albiona to death by beheading when she refuses to become his lover.
King Numedides, who Conan slew to gain the throne of Aquilonia, was a madman who bathed in the blood of virgins to gain immortality (at the advice of the equally evil sorceror, Thulandra Thuu. Conan only came to oppose the king when Numedides had him tossed in prison for being a bit too popular. He also had a dancer who Conan fancied skinned and had his men toss a scrap of her flesh into Conan's cell to taunt him.
While Thoth-Amon is sometimes portrayed as a Noble Demon or given redeeming qualities, The Book of Thoth paints him as a selfish, horrible monster. Starting as an ambitious orphan, Thoth murders his friend Amon and takes his name to steal Amon's new place in the Ibis Temple. When Thoth's mentor discovers Thoth has been worshiping the Serpent God Set, Thoth magically lobotomizes him to admit he is the 'real' heretic. Thoth has every member of the royal family in front of his chosen puppet killed to place him on the throne and magically lobotomizes him to use him as a puppet and convert all of Stygia to Set's worship, turning it into a hellhole. Thoth proceeds to have his mentor's son crucified, only rescued by the intervention of allies, and is so far gone that he considers having his friend crucified again after said friend saves his life. Thoth unleashes a plague to consolidate his power, which kills his own sister. Discovering his sister's death leads him to Jumping Off the Slippery Slope on the basis that he's already done the worst things he can.
Ensemble Darkhorse: Thoth-Amon. While a minor character who never met Conan face to face, possessing a number of redeeming traits despite being a villain made him extremely popular, so much so that any adaptions feature him as the Big Bad or an Expy of him.
Fair for Its Day: While many of his female characters were stereotypical cringing females waiting to be rescued Howard also wrote some surprisingly strong female characters: Belit, Valeria and the Devi of Vendhya. His treatment of non-whites is more disjointed and complex. On the one hand is the revoltingly racist "Vale of Lost Women." On the other hand Conan is surprised to find in "Queen of the Black Coast" that his black crewmen, who he had expected to panic and run had fought and taken a toll of the werehyenas. The black guardsman who seeks to kill, and inadvertently frees, Conan in "The Scarlet Citadel" is given a sympathetic treatment. Yes, he wanted Conan dead but for a perfectly acceptable reason - in Conan's pirate days as 'Amra the Lion', Conan had burned his village and killed his brother.
While Howard's most famous Conan villain, Thoth-Amon, was non-white and extremely wicked, he had several noble qualities; he was brave, strong, intelligent, and genuinely cared for the advancement of his people (a quality Conan wouldn't acquire til he took Aquilonia's throne).
"Funny Aneurysm" Moment: In the letters page of Conan the Barbarian #267, a reader asks for back issues of the title, and expresses regret that the title was cancelled. The editor points out that a) Marvel don't directly give out back issues and b) the title's clearly still going. That title was cancelled by #275.
Just Here for Godzilla: Many who bought the original books had no interest in reading them at all. They bought them for the lush, power paintings that served as the book covers. Courtesy of Frank Frazetta himself.
Les Yay: Numerous examples, generally on the part of villainous or 'depraved' characters.
The Valley of the Lost Women features strange women capturing and kissing the female lead in order to paralyse her.
Also a little between the Jenna and Zula in the second movie.
In Red Nails, Valeria assumes that Queen Tascela wants to drug her in order to have her way with her. She actually just want to suck her soul in order to keep her youth. There's also a scene in which Valeria whips the slave girl who tried to drug her.
Values Dissonance: The vast majority of the characters are not meant to be moral even by the standards of the 1920s. However, there are a number of instances - the treatment of women and the veiled horror at "mingled races" among them - that may grate. Howard's plucked-from-history world building method also naturally led to racial stereotypes - just try to find an honest Zingaran, a gentle Pict or an atheist Stygian. But see also Fair for Its Day.