At the beginning, whenever Vanille asks a question that anyone who lives in Cocoon should know—like saying "who's this guy?" when the Primarch shows up on the television—nobody gets suspicious. They just assume she's a major ditz.
Sazh: I mean... what are they teaching kids these days?
The opening cinematic to Chapter 12 contains one for Snow. He waves to a cheering crowd...conveniently forgetting about his l'Cie brand. Once the guards start mobilizing, he realizes what just happened.
Just before Fang gets her Eidolon, she talks about how she's made up her mind. The Eidolon appears and she says it's for l'Cie who are indecisive. Just after Snow protects her, you can hear him say, "So, you haven't made up your mind yet?"
Early on when Snow and Hope are attempting to get to Hope's house, there's a pair of civilians whose plight the player can hear of if he or she decides to get close to them. It's a father and son that were separated in the commotion. Only it's the father that starts to whine about how he should have listened to his son when he was told to stay where he was when they were separated. When you clear out the enemies and they can get together, the son will scold his much older father.
All of the guys looking away in embarrassment when Fang checks Vanille's brand. Hope covering his eyes and coughing is just sort of hilariously adorable.
Hope and Vanille falling to their deaths in the opening cinematic for chapter 11, made funnier by virtue of being a split second piece of dialogue in the middle of a CMOA.:
This one is repeatable, since it happens in gameplay, but requires some timing: do a Paradigm shift and watch your party strike their Angels Pose...followed immediately by a mob knocking one of them flat on their ass. Whilst the other two just stand there looking cool (or attempting to).
Even better when the enemy uses an attack that launches the character into the air. The ring that appears around the character when Paradigm shift occurs is there, and the camera will focus on it, but your character will be flying through the air.
If a party member is launched just before another member heals or buffs them, they have a chance of spouting their character-specific "thanks!" line... while being juggled Smash Bros. style by a Behemoth. And, of course, the simple sight of your medic desperately chucking cure spells at someone who is soaring through the air is completely hilarious by itself.
Chapter 12, the party casually jumps off a ledge, leaving Vanille to wonder what they're doing before following. The group falls through the air in free fall as Vanille waves her limbs and screams, and Lightning activates the Grav-Con Unit for them to land in safely.
Vanille: "You could have warned me!" Fang: "That's how they get around on Cocoon." Hope: "That's howLightgets around!"
Mark 34. Here comes Zenobia the Butcher, and you're expecting her to be a tougher fight than most of the Undying marks preceding her...until a fucking tonberry shows up and steals your kill. With a knife. In one hit. What. Of course, Final Fantasy veterans already know what to expect of those critters.
While wandering Pulse, you can come across some of the sheep. Vanille walks up to a larger one, grabs it, then yanks a tuft of its wool off so hard it sends the thing crashing to its side when it comes off.
Early on when Vanille is left with Sazh, she's climbing up a piece of rubble/machinery. While it isn't intentional, Sazh looks up and is about to get a full view of Vanille. The chocobo chick blocks his view and chirps indignantly.
Sazh gets one when he and Vanille go together after the plane crash. A piece of debris is blocking their path and you have to operate a machine to get rid of it. Said piece of debris comes towards them, increasing at speed causing Sazh to go:
Near the start of the game, during the battle between NORA and the Sanctum, Vanille discards her cloak, revealing a colorful outfit that seems completely out of place among the destruction around her, heads over to Hope, and hands him an assault rifle with a cheery "Here you go!", like it's a packet of sweets.
One line, uttered by our favorite funny man when he first lays eyes on the Gigantuar.
Sazh: SWEET MERCY!!
Sazh in general is great at pre-battle quotes. Meet an adamantoise?
Sazh: That thing is gonna Gran the Pulse right out of us!