Lute attacking Knoll twice after he points out she's been stalking him for a while (in their C Support). Not only does Knoll dodge all the blows and escape from her, but she comments he's dangerous just because nobody has ever dodged her blows (at least story-wise).
Lute's supports with Artur are a riot. Key moments include their C support, where Lute had tried to help Artur overcome his fear of spiders by covering him in them while he slept, and their A support, where Lute doesn't know how to react to Artur's confession of love as none of her textbooks describe what being in love is like.
L'Arachel's meeting with Eirika features L'Arachel nearly blowing the fact that she's royal, until Dozla very dramatically cuts her off. Upon L'Arachel's group leaving, Eirika lampshades their oddity — and she's still confused when she runs into them again later.
When Joshua attempts to hit on Natasha—a nun, with actual vows of chastity implied—and she is so distracted that she doesn't even notice.
L'Arachel's supports with Ephraim are all hilarious, especially when his slightly unclothed body completely breaks her delicate sensibilities. Not helped by the fact SHE was the one who asked him to let her see his scars so she could heal them.
Made even better by the fact that she specifically freaks out over seeing his shoulder... Yet L'Arachel's own shoulders are clearly bare.
Forde takes a nap in battle. Meanwhile, Vanessa is flying one her pegasus over the battlefield and spots Forde, mistaking him for having been killed or at the very least unconscious. Hilarity Ensues.
And after Vanessa sees Forde is just asleep, she throws a fit and leaves him there...and then he wakes up and just wonders if someone was there. The following support conversation is Vanessa chewing him out on this.
In Chapter 10, on Eirika's path, Innes fires the crew of mercenaries he hired to convince them to abandon him and save their own lives when they're outnumbered and under siege from an enemy army, but they refuse. The mercenary boss refuses and then tries to get his female second-in-command to flee, who cuts in:
Tethys: Would the two of you kindly stop acting like such... men? And you! You've already fired us. You can't order us to leave now.
His supports with L'Arachel are among the biggest proofs. You know she's the Tsundere of the game... and yet she brings the Tsundere out of Innes and they pretty much try out-tsunning each other. With manners.
Dozla and Garcia taking their common Boisterous Bruiser traits Up to 11 levels while trying to diversify into other classes. And the results are described in their A support...
Garcia: That did not go as well as I had hoped. Dozla: Well, that's not entirely true, is it. Garcia: It would have helped if you hadn't whacked me in the head with the staff. Dozla: I didn't mean to hit you! You just got in the way when I was...conjuring. Garcia: I still have a lump on my head. Dozla: I feel badly about it, all right? Besides, I think you're forgetting that I also healed you with that staff! Garcia: No, you didn't! You burned my beard clear off! Dozla: Oh, yes. That's right. I'm sorry.
Having Ross promote to a fighter or a pirate will solicit a couple of giggles. The kid pulls out pounds of muscle from the fucking ether, and the change between his journeyman class and both of his promotions is something you'd expect from Pokémon.
The other trainees' promotions can be hilarious, too. Try promoting Amelia into a knight, and then a general. She'll then be going around the battlefield in armor that looks like it's 3x her size.
"Armored Knight" is her class in Fire Emblem Heroes, and she uses Axes at that, which is something she can only do in her own game as a General. Her axe is also attached to a chain, which is also a reference to the GBA games' General sprites (and only the fully-promoted General), and yes, her armor is that ridiculously big compared to her body.
Then, have Ewan become a Shaman or either of its promotions. It's funny just for how completely unfitting his bright color palette is for the classes, though the Druid sprite is also easily the largest magic-wielding sprite and looks to be about twice the size of his Pupil sprite.
Ephraim's B Support with Tana. Tana tried to make Ephraim remember about how they first met... but unfortunately for her, her brother had spent that entire day (her birthday no less) dragging Ephraim around and challenging him to duels, resulting in her getting absolutely furious that Ephraim can't remember what she was wearing or what her hair was like.
On Ephraim's route, having Joshua fight Caellach has them talk about their time as mercenaries and is somewhat less emotionally charged than on Eirika's route. If you have Colm as a Rogue or Rennac steal the Hoplon guard from him and then attack him with Joshua, you can one-shot him with a critical hit, right after he claimed that he was way out of Joshua's league.
Joshua getting utterly confused and frustrated during his supports with L'Arachel, as he cheats and cheats and cheats and yet somehow she still wins.
L'Arachel finds herself enjoying the gambling with Joshua so much that she comes up with the idea of building a gambling hall in Rausten. And this is the same woman that spent the previous two supports with Joshua preaching about the immorality of gambling.
Ephraim and L'Arachel each returned home after the war, but L'Arachel visited Renais often. Over time, the two were wed. Their marriage threw Rausten into turmoil, but L'Arachel's self-centeredness carried the day.
Everything about Lute's interactions with Vanessa, starting with Lute fangirling over Titania, Vanessa's pegasus, then asking Vanessa if she could use Titania for magic training against high-resistance creatures and finally coming to a high point when Vanessa jokingly says that "The wings of a thousand pegasi are an incredibly potent aphrodisiac"...cue Lute actually trying to steal Titania's wings.
Colm tries to be an information broker for Kyle. Keyword being "tries".
Ephraim becomes The Dreaded for the Grado soldiers, and pretty much anyone else siding with Grado for that matter. Amelia believes Ephraim mistreats women and Rennac believes Ephraim is a ruthless noble, resulting in this gem should Ephraim hire him:
Rennac: You...aren't going to stab me once I take your money, are you? Once the fighting is all done, you won't burn me at the stake or anything? Ephraim: ...What rumors are these people spreading about me?
Dozla's triumphant shout when brought to the final battle is "Gwah ha ha! Same goes for me!". Obviously, this line is intended to come after L'Arachel's line (as per his character) but because of the dynamic way in which the lines are ordered, this isn't a guarantee. Dozla might say this in response to any character, including characters like Lute ("Is that the Demon King? I've read all about him.") or Tethys ("Don't tense up! You'll fight better if you're relaxed!").
When Ross gives Amelia a necklace he'd bought awhile ago from a street beggar despite not having anyone in his life to give it to, her upbringing in poverty has her unwilling to accept something so precious to him. His response to this to say.
Ross: I see. Please just take it and enjoy it. Amelia: Really? I can have it? Ross: Of course! Besides, I've always looked better in earrings than necklaces. Just kidding!
And he's just a minor character shipping with a minor character.