During a battle between the White Base and Ramba Ral, a massive storm crops up and lightning begins flashing. Soldiers on both sides, having been born and raised in space, freak out and assume that the lightning is some kind of new enemy weapon. Except for Ramba Ral himself, who has been on Earth long enough to know what it is.
On the White Base
Fraw Bow: What is that? A new Zeon weapon!?
Meanwhile on Ramba Ral's ship:
Zeon Soldier: Sir! A new Feddie weapon!
Ramba Ral: Don't panic! It's called lightning here on Earth. Although I will admit seeing it up close like this is a bit unsettling.
From Gundam: The Origin, when Kycilia Zabi recruits Char for her own forces following Garma Zabi's death, the only demand he makes of her is to give his favorite pair of sunglasses back.
Also, Kamille playing the role of the Accidental Pervert when Fa gets out of her shower...
The manga Mobile Suit vs. Giant God, AKA Gundam vs. Ideon, contains a wonderful moment. Amuro and Judau are piloting a two-seater ZZ Gundam upgrade when they get ensnared by enemies with Gundam hammer-style weapons. Amuro's response? "Psycommu Arm!", followed by the Mega Zeta performing a Newtype-controlled Rocket Punch. Judau's reaction is priceless.
The League Militaire's plan for assaulting the Kill SatKeilas Guelie: bombard it with low-level radiation that makes all the Zanscare personnel sick to their stomachs, distracting them in battle.
The episode in which Uso has been captured by Zanscare. One of their female commanders decides to interrogate him... while in the bath. After a good deal of humorous struggling, he manages to escape, and spends most of the rest of the episode naked running away from Zanscare guards and piloting his way free.
When Oliver and Marvet decide to marry, Uso is upset since he's had a Precocious Crush on Marvet most of the series. Teasing him, Marvet suggests that she should help Uso have a child, which causes Uso to go bright red and say that isn't what he meant. One of the Shrike girls then comments that Uso will find someone for himself in the future. Immediately after, Usso's best friend Shakti comes in. Uso looks at her, goes even redder, and runs away.
Uso: "I'm just happy to be fighting alongside pretty ladies."
Franny: "Oh? Then, which of us is the prettier lady? Answer me, Uso!"
Uso: *adopts a "No way in hell am I answering that question" face*
Franny and Miliera: "Answer us, Uso!"
Just the fact that, in the final battle, the White Ark is using baby Karl as a psychic radar to find Shakti is hilarious. There's one shot where Uso is actually holding him out as though he were a Shakti detector or something.
Any shot of Brandas in a space suit. The poor dog just looks completely out of his element.
Roybea buys swimsuits for the women of the Freeden. Toniya asks how he knows they'll fit. Roybea assures her that he can tell a woman's clothing size just by looking at them. Garrod and Witz immediately reply: "That's not a talent to brag about..."
And when Jamil punishes Garrod... by making him Tiffa's bodyguard for a whole day. The others's reactions are priceless.
Episode 24. Roybea, Witz, Shingo, Sara, Tonya and Kid are in a shootout with New UNE forces. Suddenly, the New UNE rolls in an IFV.
Roybea: "That's cheating!"
In the first episode, Garrod finds a mobile suit control stick in a safe and decides to sell it. Later, when his employers turn on him, he stumbles upon an abandoned Gundam X...which is missing its left control stick. Remembering the one he found earlier, Garrod says "If this works I'll believe in God!" and slams it into place, causing the Gundam to power up. He turns to Tiffa (who's just waking up after a fainting spell) and enthuses "Tiffa! I believe in God!"
Garrod just received the upgraded X Divider Gundam, and is ready to kick ass. He leaps forward heroically... and then, due to a lack of familiarity with the new controls, causes the X Divider to do a fantastic faceplant straight into the ground. One can only imagine what was going through the Frost brothers' heads when they saw that...
Just after Gato steals the GP-02, Kou takes the GP-01 and catches up to him, trying to stop him from escaping with the nuclear mecha. Upon learning that his opponent is just a rookie pilot, Gato goes into a full-blown lecture on a soldier's role in war and seeing the big picture, to which Kou instinctively responds "Yes, sir!" There's a pause, then Gato yells, "I'm the ENEMY, you idiot!"
"Attention! Lieutenant Burning is royally pissed at you!"
The B Gundam requires more explanation: Umon was a Ball pilot at the Battle of Solomon, and for whatever reason put extra armor on his Ball before the fight... that was a perfect replica of the Gundam's faceplate. However, the Ball isn't designed for the extra weight, and this causes him to go tumbling around if he isn't concentrating perfectly on maneuvers. As if that isn't funny enough, the flying Gundam head first propogates a rumor among the Zeon forces that the Gundam has been destroyed (prompting Gato to abandon his guard post, and opening a hole in the defenses for Amuro to slip through), and then propogates a second rumor that there is a gigantic 40 meter tall Gundam running around that utterly terrifies the Zeon soldiers. And, through a combination of his enemies' confusion and sheer dumb luck, Umon manages to take down six Doms during the battle.
Skull Heart also gave us the epicly ridiculous battle between the Crossbone and a bunch of Newtype monkeys flying custom Zaku's. And Tobia finally defeats them by painting the Gundam's cloak yellow and inflating it with exhaust heat into a banana shape. It's just as silly as it sounds.
The original Crossbone had another great one: Berah realizes someone is peeping on her in the shower and shouts romantic interest Kincade's name angrily. Standard anime stuff, except that Kincade, who is nearby for unrelated reasons, reacts with a startled and panicked "Yes ma'am?!" implying that it's the sort of thing he would do/has done before.
The Terran Militia's first time in space. Not only do they go bouncing all over because they're not used to zero-g, but they then get really drunk and decide that they will ride barrels down to Earth (fortunately, Loran stops that nonsense before it goes too far). Their total ignorance of how space works is just hilarious.
The Call Back to the original Gundam when the Moonrace are utterly terrified of lightning. And the revelation that the Turn A, very fortunately, is lightning-proof.
"What's so special about a turned X? A turned X is still just an X!"