The movie vs the book. The book is an anti love story, and specifically very queer focused; the unnamed narrator is gay and Holly is bisexual, they're not love interests and Holly in fact is a much different character (being based on Marilyn Monroe). The movie is a Romantic Comedy, where the two protagonists are obviously heterosexual love interests, there are new characters not in the original text, and Holly is a much more wholesome character. The jury is still out on which one is superior, or whether the movie can stand on its own even if it's basically an In Name Only adaptation.
Audrey Hepburn as Holly is another one. Fans of the book tend to think she was miscast (and she herself even thought she was) - as noted above, Holly is far more like Marilyn Monroe (who was Truman Capote's preferred choice) than Audrey Hepburn's brand of wholesome sophistication. But there are just as many who love her in the role, and her Holly has gone down in pop culture history (also noted as being quite ahead of her time by the values of 1961).
"Common Knowledge": Holly isn't actually a prostitute. Truman Capote referred to her as "an American Geisha" (which is the rare thing as acknowledging the difference between the two in American media). She attends parties and dinner dates with various men, with the expectation that she'll be given an expensive present in exchange or else "$50 for the powder room". Sex only happens if she's willing.
Fair for Its Day: While the film is notorious for the character Mr. Yunioshi, performed in yellowface as a slapstick buffoon, it does at least give him a significant profession as an artistic photographer who is much in demand by Holly's socialite circle, rather than saddling him with a stereotypical trade such as a laundry or restaurant owner. The film also aggressively highlights a mixed-race couple of a white man and a Chinese woman in Holly's party, sticking them in the middle of the frame during several sequences. This was fairly progressive for 1961.
Paul and Holly go to Tiffany's and look at jewelry, but ultimately they decide to engrave a ring from a Cracker Jack box. Instead of being offended or irritated, the jeweler gently observes the ring, then agrees to engraving it. Holly kisses him on the cheek so being so sweet.
Jeweler: I see. Do they still really have prizes in Cracker Jack boxes?
Paul: Oh, yes.
Jeweler: That's nice to know. It gives one a feeling of solidarity, almost of continuity, with the past, that sort of thing.
Holly finding Cat in the rain. Watch it and weep.
Holly and Paul finally getting together in the end, as they share a kiss in the rain (shortly after finding the cat again)!
I Am Not Shazam: The protagonist's name is "Holly", not "Tiffany" (and even less known is the fact that "Holly" actually stands for "Holiday"). "Tiffany's" is a jewelry store and the breakfast in question consists of consuming a pastry and coffee while browsing the shop window display. This didn't stop the movie from becoming a Baby Name Trend Starter for "Tiffany."
Never Live It Down: Mickey Rooney's overly caricatured and racially insensitive portrayal of Mr. Yunioshi falls squarely under this, and has been relentlessly mocked and bemoaned by modern critics and audiences.
Unintentionally Sympathetic: The film depicts Holly's curious lifestyle in a decidedly negative light, with a lot of browbeating from the other characters about how she shouldn't engage in independent frivolity, and she should settle down with one man since "people belong to each other." Her phobia of being tied down is depicted as fickle, feckless, selfish behavior on her part. The Problem? Her Freudian Excuse: She got married to a middle-aged widower when she was 13; too young to know what marriage would entail beyond "it sounds like fun." Even if the marriage was chaste before it was annulled, a middle-aged man was still grooming 13-year-old girl to become his ideal wife since he expected her to cook, clean, and be a mother to his kids — who were about her age when they got married. No wonder she has a deep-seated terror of being tied down! Any girl would be in her shoes!
Lula Mae's husband is depicted in the film as a good man who fell in love with a wild beauty who won't commit or settle down, who selfishly ran away from her loving husband and his children to pursue a life of soulless frivolity. The problem? He married a 13-year-old girl. Not only that, but he expected her to instantly settle into her role as a housewife and act as a mother to his kids—who are about her age. No wonder she has deep-seated commitment issues!
In the novella, Doc's oldest daughter Nellie, the one who discovers the starving Lula Mae and Fred in the Golightly farm's kitchen, is implied to be older than Lula Mae as Nellie refers to them as "young'uns." So Doc took in two runaway children younger than at least some of his own children and then apparently developed an attraction to one of them. He also repeatedly refers to the 13-year old Lula Mae as a "woman." While we aren't told exactly how old Lula Mae and Fred were when they showed up at Doc's farm or how much time had passed by the time Doc proposed to Lula Mae, the situation has some pretty uncomfortable undertones reminiscent of child-grooming.
Lula Mae's middle-aged husband, who married her when she wasn't even fourteen. While it's implied it was a chaste marriage (she remarks that it was annulled ages ago), and it was unacceptable (and illegal) in the 1940s/1960s, he still expected a girl "going on 14" to be his wife. It would be very hard to depict such a man as sympathetic today.
During the climax inside the taxi, while trying to convince Holly not to go to Brazil, Paul roughly grabs Holly and says that she "belongs to him," because he loves her. Considering the only romantic interactions the two were shown to have previously had was a single unexpected kiss which was implied to be a one-time thing, Paul's grossly entitled notion that just because he continued to have feelings for Holly even though she went on to get engaged to another man and presumably moved beyond their one-time kiss (she even explicitly refers to their "romance" in the past tense in one scene) is pretty hard to excuse today, even if they do become a couple afterwards. While Paul's speech about how Holly's fear of settling down in any way is running her into the ground is a significant wake-up call for her, it's still inexcusable to treat someone this way, especially when they've given you no reason to assume they are still interested in you (the opposite, in fact!)
Tear Jerker: Holly throwing Cat away, particularly her telling it "fuck off!" when it refuses to leave at first. Unlike the film, she can't reclaim him.
Values Resonance: This particular line of Holly's from the original novella, advocating Extreme Omnisexual behaviour, is especially daring for the time the story is set in (1943-4), but rings more true today:
I'd settle for [Greta] Garbo anyday. Why not? A person ought to be able to marry men or women or— listen, if you came to me and said you wanted to hitch up with Man o' War note a popular and successful racehorse at the time I'd respect your feeling. No, I'm serious. Love should be allowed. I'm all for it. Now that I know what it is.