Lysithea:[pretending to narrate a letter] “My dearest mother and father, today I had ice cream for lunch and I brained the Prince of Faerghus with a door. I guess tomorrow I'll trip and spill hot soup on the future Emperor so none of the three most important heirs on the continent feel left out."
Chapter 19 reveals a Noodle Incident in the past that one of Jeralt's mercenaries got so drunk, he sold his and Byleth's services to Acheron, of all people.
Jeralt: You know Robb's never going to let you live this down, right? Byleth: He can bloody well try; I still have the high ground. For one thing, Yuri is not the Weathervane and can't possibly be as bad as him. And for another, I wasn't so drunk I offered our services as his bodyguards for the equivalent of one night's dinner at a high class inn.
Chapter 51. Byleth is talking to Rodrigue and Seteth after revealing Agartha's existence to the Cavalry. Agreeing to legitimize Dimitri's ascention to kingship, Byleth inquires as to why Rufus Blaiddyd isn't leading the army, to which Rodrigue (of all people) drops this one liner-
Rodrigue: Rufus Blaiddyd has the military sensibilities of a drunk, concussed wyvern.
Sylvain: So about you and Claude- Dimitri: Really? Really?! Sylvain: When did that happen? How did that happen? Dimitri: Are we really talking about this now?!
There's the added fact that Sylvain actually thought Lorenz is involved between him and Claude in the relationship, much to Dimitri's exasperation and horror.
"Do not let any of the army commanders escape; they've fled from battle enough times already!" (when asked 'who goes there' by Hevring) "The King of Faerghus, who you would depose." (when ordering that Hevring be put in the prison wagon) "...keep it away from Emile's when we move back to camp. I wouldn't want to subject him to this man's mad ramblings."
Agarthan: B-But they're savages who would strip the flesh from our bones and cook it and use our bones for dreamcatchers or – or other occult knickknacks! Claude: ...It's a note of how disturbed I am to find a on-field mage younger than Lysithea that I'm only mildly appalled at being accused of cannibalism.
Sothis' reaction to Felix and Bernadetta finally confessing in Chapter 69.
Sothis: This needs to be made a fable, I need to see his face when the copies are printed and become popular with all the starry-eyed girls looking for true love.
Tiana finally gets to properly meet Rodrigue's sons and then Felix asked if she taught Claude how to fight while Glenn greeted the queen politely, leading to this exchange.
Tiana: So Glenn got the manners and you got the lack of common sense. I wondered how that would work out. Felix: I got the lack of common sense?! This moron went to war with a city state with a preteen for back up while living as a vagrant and I got the lack of common sense?! Glenn: Are you ever going to let that go?
The utter chaos of the other students reacting to Byleth's pregnancy and learning about Byleth, Claude and Dimitri's relationship in chapter 88. With many students being particularly miffed at being Locked Out of the Loop about their relationship.
How did the other students learn of Byleth's pregnancy and her relationship with Claude and Dimitri? They learned about it from Flayn.
When the combined armies finally raid Shambhala, they find out that travel between levels of the multi-tiered underground city is done via large elevators. And they can only hold several dozen soldiers at once. Byleth muses how the bards would work this into their poems about the battle in the future.
