Darkness-Induced Audience Apathy: The book and movie pile so many disgraces on the protagonist Tita, make her Love Interest Pedro so spineless and selfish, and reduce the other characters (specially Tita's big sister/Pedro's wife Rosaura) to such unlikeable assholes... that many readers have given up mid-reading/mid-watching, since it's a chore to read/watch and wonder "what's gonna happen to her now?!"
Freud Was Right: Tita has a flashback of the time she and Pedro briefly fondled each other, where she is implied to have felt his "red-hot coal" while she's holding a sausage.
Moral Event Horizon: Mama Elena goes past that line when she beats her own daughter, breaks her nose, then calls her a crazy Lunatic.
Strangled by the Red String: Pedro suddenly asks Tita to marry him and they're suddenly madly in love. Even though he betrays her by marrying Rosaura, which makes her get angry at Rosaura, she's not mad at him (that is, when she finds out why he married Rosaura). He accepts Mama Elena's decision to send him and his wife and son away to Texas and Rosaura's decision to continue the family tradition, even though they're both bad decisions and hurt the woman he loves. He comes across as rather spineless and useless, yet Tita still thinks the sun shines out of his lily-livered ass.
One of the worst offenses in the book is a scene when the already married Pedro sums up the courage to give Tita some roses. Yes, it gives the repressed, abusedTita some solace... but Rosaura runs off crying at the scene. With Mama Elena's disapproving glance, he is frightened off to go comfort Rosaura; however, it's portrayed as a cowardly thing that he goes to comfort Rosaura after, oh you know, giving a gift of love to someone else that he never gave to his own wife.
It does not help matters in the film adaptation where Rosaura is given a few more human moments, such as one where she reaches out to Tita and genuinely is grateful they get along.
Unintentionally Unsympathetic: Pedro only marries Rosaura to be close to Tita, neglects his wife so badly that it furthers her increasing Jerk Assery and ultimately destroys her and Tita's already shaky relationship, causes Tita quite the misery as well due to his selfishness and his stalking of her (which she doesn't forget to call him out on), and years later bullies and pressures Tita when Nice Guy Dr. Brown shows interest in her, etc. He is supposed to be Tita's One True Love and the right guy for her... WHY? Rosaura's death fixes it all and he is only remorseful because he was not there for Tita, but he gives little to no consideration for what he did to his late wife. (And does he even give a damn toward the deceased Roberto and his little sister Esperanza, his own children?)
Pedro's fondness for his daughter is mentioned incredibly briefly like Informed Love as Esperanza does become a reason why Pedro is wary of leaving Rosaura. It takes Tita to call out on his disregard for both of them, for him to realize his (unshown) affection for Esperanza.