Mia stabbing Lana in the chest with an ice cream cone after Lana insults Tina. Doubles as one for the film.
Phillipe helping Helen and Mr. Gianini elope to Mexico and avoid the tawdry, expensive Shotgun Wedding that his mother Clarisse has arranged.
Michael telling off Lilly for harassing Mia about being a Princess in the first book, showing the amount of knowledge he has of the Genovian government and its history and noting that Mia's father is the opposite of a Upper-Class Twit; later calls out Lilly as being jealous of Mia for changing her hair, being a princess, and for getting a new friend and calls her vain.
Pardon me, Lilly, but it's my understanding that Mia's father works extremely hard for his country. His father's historic pledge, after Mussolini's forces invaded in 1939, to exercise the rights of sovereignty in accordance with the political and economic interests of neighboring France in exchange for military and naval protection in the event of war might have tied the hands of a lesser politician, but Mia's father has managed to work around that agreement. His efforts have resulted in a nation that has the highest literacy rate in Europe, some of the best educational attainment rates, adn the lowest infant mortality, inflation, and unemployment rates in the Western Hemisphere.
Grandmere smacking the "Blind Guy" after helping to escort him across the street and revealing him to possess great eyesight.
Mia ripping Lana's (fake, but she didn't know that) braid off for calling Perin a hermaphrodite.
Mia's speech when she runs for student body president.
Lana even later acknowledges it was an awesome speech, and in book 9 recommends Mia to speak to the Domina Rei. Mia kicks it out of the park with her speech about Princess Amelie, a sixteen-year old princess who ruled during the Black Plague, saved lives despite her uncle attempting to usurp the throne and burn her proclamations, and mandated that Genovia become a constitutional monarchy in her last proclamation.
Mia becoming a published novelist at the age of eighteen.
Olivia leaving her aunt and her family to live with Mia and their father. Even better was "The Reason You Suck" Speech she launches on her aunt for restricting her life, stealing the money meant for her, and for caring more about her carpet than her bleeding niece:
No! Of course not! I don't want to live with you because all you cared about when I walked in was getting the stain out of your stupid carpet. They cared about what happened to me. That's why I want to go live with them.
Grandmere's Death Glare aimed at Olivia's Uncle when he objects to the girl having a dog, due to his allergies, given that he's a huge bully that aligns himself with other bullies and is raising kids a lot like him, it's quite awesome to see him cowed by just a look from her.
It's revealed in Olivia's book that Genovia is suing her bully's father, a lawyer who basically lets his daughter get away with murder by threatening litigation against their private school, that girl and her father are no longer a Karma Houdini pair.
From the films:
From the second movie, after Viscount Mabrey has staged a humiliating accident while Mia was inspecting the royal guard and Joe has figured out he was behind it:
Joe: Viscount, you may not be aware of what my job entails as the Royal Head of Security. My job is to protect the crown. To make sure no harm comes to the crown. To step in when someone toys with the crown's emotions.