The ending to episode 9. After spending the entire episode repeatedly foiling the Big Bad's plan only for him to reveal that he has a backup plan, he reveals his final trump card and all seems lost... Then Flonne shows up out of nowhere with a Humongous Mecha which proceeds to push the moon back into its original orbit. Made even more hilarious by said mecha even getting its own transformation-scene.
On TGS Press conference, Prinny took the stage and welcomed everyone to the show. As he waved his flippers about, he called NIS President Souhei Niikawa onto the stage. Turns out he was cosplaying as the prinny itself.
This video (provided by GamesRadar) talks like a cheesy salesman trying to sell his snake oil, but the ad is so over the top it loops around to freakin' hilarious. "Take a dump on the face of common sense"?! What are they smoking, and where can I get some?
A similar event involving Valvatorez and Prinny Kurtis. Val notices the lack of "dood" in Kurtis' speech, and fights him after he refuses to say the word. He complies afterward, but gets annoyed when Fuka, Desco, and Vulcanus share their opinions of how cute it makes him sound, due to wanting to maintain a cool image.
Fenrich's big lie that Axel is the anarchist trying to rebel against the government. It works without a hitch, helped by the fact that Valvatorez believes it wholeheartedly.
Also everyone's reactions to the reveal of Vulcanus' identity, as well as the reveal itself, for that matter. Flonne accidentally blows Artina's cover right up, literally minutes after she makes her appearance, and completely casually, to boot.
Genjuro, Fuka's dad, takes Fuka's death and return rather calmly...
Fuka: What the hell are you doing, Dad!? Have you teamed up with that Nemo guy!? Are you trying to destroy everyone!?
Genjuro: Huh? I saw there was girl wearing a weird hat, but I didn't know that girl was you, Fuka.
Fuka: Huh!? You JUST noticed me!? I'm your daughter!
Genjuro: Fuka, what are you doing here? I thought you went to Hell.
Fuka: What...!? How can you say that about your own daughter!?
Genjuro: Well, you're not the Heaven-type, you know?
Fuka: Urrrgh! What the hell's your problem!? Plus, I'm not even dead! Are you telling me that I died!?
Genjuro: Yup, you died. You definitely died.
Also, after Genjuro explains that the creation of Desco and Des X was so that Fuka could have a sister, it seems that the family's issues might be resolved...then Fuka goes on a rant on how she didn't want her sisters to be killing machines.
You know what, the ENTIRE scene with Genjuro is freaking hilarious.
In one of the DLC cut scenes, a talking sardine shows up for the interview and Valvatorez couldn't be any happier. That is until it's revealed that it's just Ash confining himself to it. Valvatorez is absolutely devastated.
In fact, anytime Valvatorez goes into party a rant about the power of sardines.
Watching an unprepared player's entire party being wiped out the moment they are brought of the base panel against Baal thanks to his deadly new evility. Sure, it sucks for the player but it's utterly hilarious to watch, especially the first kill which often has players stare at the screen in total disbelief over what the hell just happened.
Valvatorez lecturing Desco on how a Final Boss should act, that it is not done to immediately kill all the heroes without first receiving their attacks in a dignified manner. Dealing lethal damage on your first turn completely ruins the balance of the game! Desco's constant switching between Large Ham and Moe during the whole scene is also bound to make you smile.
Read the entry above, about Baal, and his ability that kills any unprepared character THE SECOND that it takes the field, and you'll realize that the line about that not being done is Hypocritical Humor.
In episode 3, Fenrich announces to everyone that Valvatorez is going to take over the regime and kick out the President. Everyone is surprised, including...Valvatorez himself?
Emizel: T-Take over the regime!? He's planning to defeat my father and take over the corrupternment!?
Fuka: You are...!?
Valvatorez: I AM!?
Fuka: Why do you sound so surprised!? Didn't you know about it!?