Lina's Voice (Dramatic Irony)
A central irony of the film is just how obnoxious Lina Lamont's voice is contrasted with the fact that she has no idea and thinks she is an elegant and refined actress. Dramatic irony occurs when the audience realizes something that the character does not. Thus, when Lina expresses indignation about the fact that no one will let her talk, the audience laughs because they realize the reason no one lets her talk is because her voice is so shrill and annoying. She is in the dark about this, however, and spends much of the movie unaware of her limitations as a speaker, singer, and actor.
Lockwood's Biography (Dramatic Irony)
Lockwood tells his story to the crowd gathered at the premiere of The Royal Rascal and describes his magnificent journey to the top. Ironically, the story he tells of his silver-spoon, highbrow upbringing doesn't match the truth that he came up through the rather rough-and-tumble world of vaudeville, and that he only ascended the ranks to become a movie star because he happened to be on set the day an actor was knocked unconscious and he stepped in as a stuntman. The dramatic irony comes out of the fact that we the viewer can see that Lockwood's story does not match up with the montage of what happened, but the crowds assembled at the premiere cannot. They believe his every word, even as he professes that his main motto is, "Dignity, always dignity," but we can see that much of his life has been anything but dignified.
Nobody Thinks "Talkies" Will Catch On (Dramatic Irony)
At the party at Simpson's house, a film is shown where a man announces the invention of the talking picture. The members of the audience, a group of silent film people, do not believe the movie at first, and even suspect that someone is behind the screen making the sound. Then, when it is revealed that talking pictures are a real technological advancement, no one at the party seems very fazed or intrigued. In fact, many remain skeptical that it will ever catch on. The viewer, themselves watching a talking picture, knows that talkies do indeed catch on and revolutionize the form, so the party guests' skepticism strikes us as ironic and humorous. Thus, we have another instance of dramatic irony, in which the audience knows something that the characters do not: that talking pictures will soon become ubiquitous.
The Raising of the Curtain (Dramatic Irony)
At the end of the film, Lina pretends to sing "Singin' in the Rain" while Kathy does the actual singing into a microphone behind the curtain. This gives the illusion that Lina has a nice voice, which itself creates a kind of irony, because we know this is not the case. However, another instance of dramatic irony occurs when Lockwood, Cosmo, and Simpson raise the curtain to reveal that it is in fact Kathy doing the singing. For a moment, Lina has no idea that the curtain has been lifted, and the audience begins to laugh. They can see that the singing is all an act, but she has no idea why they are laughing. Slowly she turns around and realizes that she has been exposed as a sham.