Irony of Keeping Quiet
Ramona has overheard her teacher describe her as a nuisance and a show-off, so she is determined to not attract attention to herself. This leads her to keep quiet about her nausea until she throws up in class, which ironically attracts far more attention than if she'd asked to be excused to go to the nurse's office.
Irony of Responsibility
Although Ramona is only eight years old and has no authority over the four-year-old Willy Jean, she is blamed for everything bad Willy Jean does. The adults who are supposed to be watching Willy Jean elect not to do so, but they do not consider themselves responsible for the consequences since it's easier to blame Ramona.
Irony of School Work as Escape
To avoid Willy Jean, Ramona insists that she has to do her Sustained Silent Reading or SSR, which is a form of homework. This is a strategy that her older sister Beezus uses often to avoid having to babysit. Whereas school work or homework is supposed to be unpleasant, compared to babysitting Willy Jean it's ironically something Ramona is anxious to do.
Irony of the Pink Eraser
In the 1970s and 1980s, when this book series was written, most erasers were pink. When Ramona's father gives her a new pink eraser, he's actually giving her a fairly ordinary item. This is evidence that the Quimby family is not wealthy and that money is tight, possibly due to Mr. Quimby's need to go back to university to continue his education. Ironically, Ramona treasures the pink eraser and becomes very upset when it is stolen by a boy at school.
Irony of the Egg
In the era when this book was written, it was common for children to bring bagged or boxed lunches from home to eat. Children would compare the contents of their lunches and occasionally trade. Some items were considered trendier or more fashionable than others. This year, hard-boiled eggs, in the shell, were considered the fun treat that everyone wanted. Kids would crack the shells, peel off the eggshell, and then eat the egg. When Ramona found an egg in her lunch, she naturally thought it was hard-boiled like the others, but in reality her mother had either forgotten to boil it or gotten it mixed up with the hard-boiled eggs. This happened, ironically, on the day Ramona decided to be extremely cool and adventurous, by cracking the "hard-boiled" egg on her head. When the egg breaks and gets in her hair, Ramona ends up being humiliated because of the same food item that was supposed to make her popular.
