From Volume 18: Ropponmatsu 2 is malfunctioning and Iwata barges in, declaring her to have revealed herself as "A juvenile who gets violent easily" before spouting nonsensically "A message to YOU Rudy!". He then attempts to transform like a Sentai hero, with Sumiyoshi screaming at him not to for fear of his home being destroyed. And then...nothing happens. Iwata's reaction?
Iwata:"I can't Bio-Boost?!" Sumiyoshi: (Ashamed of himself) <Damn. I actually expected him to transform.>
From volume 1: An NHK collector shows up at Excel's and Hyatt's apartment to collect a bill. Hyatt successfully scares the man away by answering the door while coughing up blood.
From the detective show parody in the manga:
Iwata: (Having seen Ropponmatsu kill Watanabe) You murdered hi... (Ropponmatsu puts a fist through a wall)
Iwata: I mean... the murderer can't have gotten far! Ropponmatsu: (Disturbingly cheerful) I'll bet they kill again!
From the same story, Excel being pursued by the police... and the police chief (Played by Dr Iwata) shows up engaging in a shoot-out with his own men, screaming how they'll "Never take him alive" for no reason. This is shortly after the scene where he shows up in a tank, hoping to kill Excel and win a free meal.
Dr Iwata: Sorry boys, but them short ribs is MINE.
Volume 19, after spending the entire volume looking for Excel, the only person who can prove that the Excel hanging around with Il Palazzo is a fake, the first thing Elgala says when she finally sees Excel:
From volume 20, the elderly priest's reaction to seeing that the "sacred tree", a holy shrine at his temple, has been carved into a replica of Lord Il Palazzo.
Volume 21, a scene that makes fun of all the unintentional (on their parts) Les Yay between Excel and Elgala. They're drowning in a flood, and Excel suddenly seems to give Elgala a passionate Underwater Kiss. After they get out it turns out that she sucked all air out of her lungs, and still has the gall to complain about her passing out.
Kabapu, who's lost all his money by this point, invites his team to a fancy dinner to celebrate them finding a gold bar that's put him back on top. He starts shaking a bottle of champagne to which Misaki notes she can "Hear each finger bone cracking". As Kabapu wrestles with the bottle at crotch level it quickly escalates to Does This Remind You of Anything? as the cork bursts off and the champagne pours out in perhaps the most horrifyingly suggestive way EVER. This is punctuated by Kabapu declaring "I AM CORRUPT" and the joint reaction of the others: "This is NEWS!?" The best part is their expressions. Watanabe's rictus grin, Iwata's slowly dawning horror and Misaki looking away in disgust.
Kabapu is a great source of these. See also his hot springs vacation where suddenly the manga becomes a murder mystery with no resolution and a random appearance by a very violent Columbo expy.
And his mayoral election video. Perhaps the most nausea inducing sight ever, as a man who's basically the devil himself tries to appear "Humane".
Damn near everything Excel does but her and Elgala's fights are a mix of fan service and hilarity. Then there's her decision on going out of the apartment:
Excel: We'll use the fire escape to confuse observers!
Elgala: FOR GOD'S SAKE SENIOR!
Everyone assuming that Sumiyoshi is sleeping with Ropponmatsu 2 because she's malfunctioning, causing her to pounce on him and then have to be tied up.
When Elgaga is officially introduced in vol. 8 Note (she had briefly appeared in vol. 7 but wasn't part of ACROSS then), she wants her nickname to be Eh-chan. Excel immediately protests, saying her nickname is Eh-chan. Elgala suggests Excel call herself "Ex-chan" instead. What follows is a parody of Reservoir Dogs:
Excel: Some other guy on some other job is called "Ex-chan"! You're "El"!
"Herro! Merry Christmas I am, uh, Exceru! You ah dog!"
In the English dub, this is turned into equally-as-amusing Gratuitous Spanish: "¡Me llamo Excel! ¡Feliz Navidad! You're my bitches!"
From the first episode, "THE BULLET OF JUSTICE CAPS EVIL'S ASS!"
And then at the end Good Excel gets arrested for shooting Evil Excel.
There are a lot of these in just the first episode. Excel knocking people into space with her schoolbag, having to restart a scene repeatedly because she WON'T SHUT UP and then there's her mission to kill the artist of the series, then the shoulder angel fight, then her stint as a traffic director...oh my gosh, there's too many to list as a whole!
This bit, after Pedro reveals he's homesick:
Excel: Pedro, you idiot! (punches him twice) Pedro: ......Miss Exc- Excel: (punches him again) ONE MORE TIME!!!
At the start of the sports episode, we get the sight of Ilpalazzo waving a tiny flag and saying, in the most deadpan voice he has ever used, "Japan."
At the end of the same episode, it looks like Excel's going to get the chute yet again. Instead, as she starts to deliver her report, she accidentally lets go of the bowling ball she's waving around for some reason. Il Palazzo looks up just in time to see it an inch from his face as the screen goes black.
Hyatt, upon seeing Excel Kobayashi and Mikako Hyatt:
Hyatt: (sounding sweet as usual) Those imitations are quite annoying.