What is an instance and explanation of irony in chapter 27 in To Kill a Mockingbird?

In chapter 27, Bob Ewell loses his job working for Works Progress Administration after he was fired due to laziness. While everyone else in the town had struggled to find a job in the 1930s, Ewell had stayed unemployed and instead lived on welfare checks during the Depression. According to Scout:

Mr. Bob Ewell acquired and lost a job in a matter of days and probably made himself unique in the annals of the nineteen-thirties: he was the only man I ever heard of who was fired from the WPA for laziness.

After he is fired, he begins collecting his welfare checks again, and at the welfare office Ewell tells Miss Ruth that Atticus had gotten him fired. Ewell is later humiliated by Atticus, who proves him to be a liar after his testimony contradicts his daughter’s, whose own testimony eventually proves Robinson could not have committed the crime. This is ironic, as the expectations or perceptions of an event are very different from what actually results. Ewell lies about Atticus’s involvement in losing his job, then gets caught in a lie. Ewell lied in an attempt to make himself look better, without realizing he ends up looking like the fool he is known as in town after the trial.
Atticus underestimated Ewell’s capacity for evil. This is ironic, as Ewell is the town fool, known by all to be lazy; he is a racist liar, yet he has the power to accuse Tom Robinson due to his white privilege. This combines the elements of tragedy and irony (tragic irony), as Tom Robinson is eventually gunned down after attempting to escape. The incidences of irony in chapter 27 can be interpreted as contributors to the moral lessons conveyed in the story associated with honesty, justice, and equality; Harper Lee wrote the novel during the Civil Rights movement, in which black people sought to gain equal rights under US law.
Irony can serve a variety of functions; it keeps readers engaged in the reading experience and stay invested in the story; furthers suspense and makes plot points more interesting; creates surprising outcomes and plot twists; provides the reader knowledge, such as character motives or an allegorical lesson.