One of the most common movie tropes is when a villain has a final monologue. It usually happens when it looks like the villain is about to win. The hero seems defeated, and the villain takes some time to gloat and describe the finale of their master plan, what they're going to do to the hero, or other details.
Whatever they talk about, there have been movies in which the villains didn't know when to stop their monologue. As such, they eventually lost because they were either talking too long and got distracted, or their monologue provided the heroes with just the information they needed to know.
5 Khan In Star Trek II: The Wrath Of Khan (1982)
When a villain spends years, sometimes decades planning their revenge, they're more inclined to monologue away their victory. Khan Noonien Singh holds a deep grudge against Kirk after Kirk had him stranded on a planet. When Khan finally catches up with Kirk, it's not enough for him to endanger the whole crew. When it looks like Kirk and his ship are finally finished, Khan doesn't destroy them right away. Instead, he makes sure that Kirk knows exactly who's responsible for his upcoming demise and why.
Khan's need to have the last word gives Kirk and his crew enough time to solve the problem, and they're able to defeat Khan in the end. Considering that Khan believes himself to be superior, both physically and mentally, to Kirk and other humans, the fact that his hurt pride and emotions cost him his victory makes the movie's finale even more ironic.
4 Darth Sidious In Star Wars: Episode VI: Return Of The Jedi (1983)
Even a series as legendary as Star Wars didn't avoid the danger of falling into the "villain monologues their way to defeat" pit. Darth Sidious has a great experience when it comes to dealing with people but despite that, he fails to recognize that messing with a family isn't a good idea. After failing to convince Luke Skywalker to join the Dark Side and kill his father, Darth Sidious hurts Luke and then mocks him and keeps on talking, until Darth Vader regains his strength and decides enough is enough.
In a surprising moment of defiance (for Darth Sidious, at least), Darth Vader deals with Darth Sidious, making it clear that the power of family bonds is sometimes even greater than the calling of the Dark Side (even though Kylo Ren might not agree with this assessment, considering the fact he murdered his father).
3 Scar In The Lion King (1994)
The classic animated movie The Lion King is another excellent example that even the villain's monologue that leads to his defeat doesn't always diminish a movie's overall quality. Throughout the movie, Scar does well when it comes to fulfilling his evil plan. He's responsible for his brother's death, forces the young Simba to leave, and becomes the new king. That's not a bad score for the ambitious villain, but Scar ruins his potential victory for himself.
After Simba comes back to get the throne, as is his right, Scar almost kills him...but not before telling Simba the truth about how his father died. Unbeknownst to Scar, hearing the truth is exactly what the seemingly defeated Simba needs to regain his energy, and he ends up triumphing over his evil uncle.
2 Syndrome In The Incredibles (2004)
The victorious villain monologue most commonly appears in superhero movies. The Incredibles successfully make fun of superhero tropes and clichés, but they contain a villain monologue as well - one that costs Syndrome his triumph. At least the movie points out the danger of preaching to the heroes, as Syndrome previously stops himself from launching his monologue at Mr. Incredible. The determination not to tell any superhero his master plan doesn't last, though, and in the movie's ending, Syndrome doesn't resist the temptation of an epic monologue.
After Jack-Jack beats him thanks to his newly discovered powers, Syndrome doesn't run away but confronts the Incredibles instead, threatening them. That doesn't work out so well since it provides Mr. Incredible with the opportunity to deal with Syndrome once and for all.
1 Ronan In Guardians Of The Galaxy (2014)
Despite its popularity, the MCU has created some over-the-top villain monologues over the years. A good example is Mysterio's monologue in Spider-Man: Far from Home (2019) in which he talks about his master plan in great detail and takes the time to thank every single person who worked on the plan. But at least Mysterio didn't monologue his victory away like Ronan the Accuser did in the first Guardians of the Galaxy movie. When Ronan encounters the Guardians on Xandar and emerges intact from the fight, instead of using the hammer to destroy Xandar, he launches into a lengthy monologue.
That gives the Guardians enough time to find their footing and decide how to distract Ronan from fulfilling his plan. In the end, Peter Quill does it by erupting into dance and song, making it one of the most bizarre movies in the MCU. By the time Ronan comes to his senses, the Guardians figure out what to do and as a result, Ronan is defeated.