In Heir to the Empire, Leia goes to Kashyyyk and is greeted by a Wookiee who she can comprehend perfectly, after years of not being able to completely understand Chewbacca. This leads her to assume that Chewie had a speech impediment that he'd never told her about, which Chewie finds absolutely hilarious. It's up to their new guide to explain that Chewie speaks perfectly; it's the guide who has a speech impediment, of a type that humans actually find easier to understand.
Undermined a moment later, when he reveals that he was used as a go-between for Imperials taking Wookiee slaves off Kashyyyk.
Han's Accidental Misnaming moments with the Noghri on Myrkr in The Last Command when they call him "Consort of the Lady Vader" and later "Han clan Solo".
Thrawn's Sarcasm Mode: "Thank you, Ferrier. Your approval means so very much to me."
The exchange between Han and Lando when calling back to the last time Lando flew the Falcon.
The pause symbol vanished before Thrawn could answer; but it wasn't the standard quarter-size figure that replaced it. Instead, a huge image of C'baoth's face suddenly glared out at them, jolting Pellaeon an involuntary step backwards. Thrawn didn't even twitch. "Good morning, Master C'baoth," the Grand Admiral said, his voice mirror smooth. "I see you've discovered the Emperor's private hologram setting."
Luke and Mara end up escaping a Star Destroyer ("Let's not try going through the garbage compactors."), which coincidentally has also captured the Falcon. After they make their escape, Mara notices a red light on one of the panels, and gets up to fix it. Luke's response? "Don't bother. Han's got this whole ship so crosswired it'll fly with half the systems out."
Karrde proves that, whether he wants to admit it or not, he fits in perfectly with our heroes and their Crazy Enough to Work attitude. He tells Luke to take the top turret in the Falcon, as he's "reasonably sure" he get the pursuing TIE Fighters to concentrate their attack there. Luke has no idea how Karrde plans to do that, until he gets strapped in and fires up the turret. . . and sees that Karrde is flying the Falcon over the Chimera's thruster nozzles, meaning any TIEs trying to attack from below will be subject to Weaponized Exhaust.
Niles Ferrier, banking on some previous shared history, manages to trick Han and Lando into a meeting with him by faking it as a request from Luke. Later they discuss the possibility that Ferrier had planted a tracking device on their ship, and how best to get rid of it.
Lando: "Well unless you want to throw it onto another ship on our way out, we'll just have to take a detour to drop it."
After Mara was wounded in the battle for the Katana fleet, she wakes up months later in a Coruscant medcenter. Ghent, a slicer Karrde had loaned the New Republic, has been watching over her, though he's such an oblivious computer nerd Mara hardly feels reassured. When Mara asks him how the war is going, he distractedly replies that "the Empire's been making the usual trouble." Later, Mara learns what's actually been going on: Thrawn's using quick-grown clones to bolster his forces and start up a new major offensive against the New Republic. Wryly, Mara notes that she should have realized anything that got through Ghent's bubble of obliviousness must be really important, even if the slicer himself doesn't recognize it as such.
A small moment in Heir to the Empire, but when Luke and Mara are stranded in the jungle of Myrkr, Luke reveals he hid his lightsaber inside Artoo (the same as he did to smuggle it onto Jabba's sail barge in Return of the Jedi). After Mara comments on always wondering how he did that, she gets an idea and says they "need to do something about his face". Luke then wryly observes that he doesn't think Artoo has a place to hide that. Her actual idea (after having Artoo record a message from Luke to send to Han, Lando, and Karrde) is also funny in a Black Comedy fashion—using a poisonous shrub to make Luke's face break out in a horrible rash, thus hiding his identity from Thrawn's Imperials. To top it off, the comic book adaptation of this moment gives Mara a deliciously evil grin when Luke has an off-panel scream reaction to the shrub.
Partway through The Last Command, Ghent, Karrde's slicer (hacker) mentions mid-conversation with Leia that he's figured out how to crack "Delta Source", the security leak that's been giving the Empire vital New Republic intelligence. Hilarious because 1) he just drops it in the conversations as casually as if he was discussing the weather, and 2) when Leia asks why he thought to do it, Ghent responds that he did it because he was BORED.
Ackbar invoking the Ascended Meme (before memes were a thing): "It appears to be a trap."
In the first book, it's noted that smugglers don't want to work with the NR because they're afraid it's a trap.
Ackbar: Because of me, no doubt.
Mara's Flat "What." when she finds out that Luke is the Son of Vader.