Saito being told that he could kiss the princess, only Louise didn't specify that he should have kissed her hand.
In the anime, when Cromwell weakens Kirche and Tabitha with the Ring of Andvari, he gloats about how he is undefiable with it... only for him to be struck unconscious by Guiche who just happens to wander by.
Midway through Volume 9, Louise is preparing to seduce Saito while wearing the sailor uniform. She begins acting out a scene where she imagines Saito's reactions to her. Then Saito and Siesta walk in while she's acting out Saito licking her shoes, making her so embarrassed that she tries to jump out the window.
Volume 12, when Siesta invokes her right to use Saito for a day, and sets up a newlywed scenario. She asks Saito if he wants dinner, a bath... and at that point is interrupted by about half the school's maids who are eavesdropping. Siesta has to stop to drive them away (including banging on the walls and throwing a chair next to the window), then tries to continue as if nothing happened.
Everything involving the love potion shortly after that. Especially Louise still using tsundere-type lines even when under its influence.
