Daphne and Josephine are Men (Dramatic Irony)
Dramatic irony occurs when the audience knows more than the characters they are observing. This disconnect allows scenes to play out on two different levels; while we the viewer know the truth, certain characters remain ignorant. In Some Like it Hot, the central dramatic irony, that Joe and Jerry disguise themselves as women, is not only important to the plot, but also to the film's humor. Throughout, the viewer knows that "Daphne" and "Josephine" are really Joe and Jerry, but this fact goes over the heads of nearly every character. All of the members of Sweet Sue's band take "Daphne" and "Josephine" at their word, treating them as women. The dramatic irony is that we know that these two men are being interpreted as women. This dramatic irony is continually pushed to its limits, as characters like Sugar note "Daphne's" large arms and small breasts, but the truth eludes everyone until the end of the story Additionally, Osgood Fielding mistakes "Daphne" for a woman to the extent that he proposes marriage. He has no idea that he is proposing marriage to a man, and much of the comic tension comes from his naivety.
Jerry Loves Drag (Situational Irony)
Another layer of irony that comes with the cross-dressing is the fact that Jerry takes to it so easily, even though he was reluctant about it at first. When he and Joe are first walking down the train platform in drag, Jerry confides in Joe that he doesn't think he can go through with it, but once he is on the train, he is very good at playing his part, and takes on a whole new persona, giggling and gossiping with the women like sisters. As they spend more and more time in drag, Jerry gets more and more comfortable with it, to the extent that he begins to believe that he is actually a woman, accepting a date with Osgood Fielding, dancing with him all night, and even accepting his marriage proposal. Back in the room, he tells Joe that he's engaged. When Joe asks, "Who's the lucky lady," Jerry lies on the bed in a daze and sighs, "I am!" While drag did not appeal in the beginning, Jerry eventually comes to relish his new female persona.
"Nobody's Perfect" (Situational Irony)
The closing line of the film is one of the most famous in the history of Hollywood. The unexpected humor of the line derives from its situational irony. Throughout the film, a relationship has been built up between Osgood and "Daphne" in which "Daphne" is a giddy girl and Osgood her relentless admirer. Joe keeps telling Jerry/"Daphne" that all the wealth and security offered by a marriage is impossible because Daphne is, after all, a man, and two men cannot get married. This is a huge disappointment for Jerry, who really wants some of Osgood's money, and is consumed by his role as "Daphne." When they are riding out towards the yacht, escaping from Little Bonaparte's men, Jerry finally reveals to Osgood that he is a man, expecting the revelation to change anything. Osgood remains completely unfazed, however, insisting that "nobody's perfect," and implying that he loves "Daphne" so much that he doesn't even care if she's actually a male upright bass player named Jerry.
Sugar Pretends to Be a Society Girl for "Junior" (Dramatic Irony)
In order to impress her new millionaire friend, "Junior," Sugar pretends that she too is from a high-class background. She tells "Junior" that she went to a prestigious college and that she used to be a debutante. When they get out to the yacht, she pretends that she knows some things about boating, but it comes out in naive inaccuracies. Just as the viewer knows that "Junior" isn't a millionaire at all, but is Joe in disguise, we know that Sugar isn't a "Bryn Mawr girl" but a regular girl from Ohio. The doubled dramatic irony makes for a particularly comic dynamic.
