Luigi upon being offered decaffeinated coffee: "I will shoot you in the FACE!"
Luigi again: "I will find a hole and fuck it!" combined with him doing pelvic thrusts into his hands (with his thumbs and forefingers in the shape of a vagina) and a "sproing!" sound effect in the background.
The context of that quote is just as funny; Luigi honestly thinks that's a good reason for Rotti to make him the heir of Geneco.
And again. "What's this, rat piss?!" STAB STAB STAB. In fact, Luigi, Pavi, Amber and Mag all act like children during the scene. Mag seems less concerned with the fact that Luigi is stabbing the attendant to death and more with the embarrassment of the thing, and Amber acts like some smug, slightly-older brat who, for once, has the high ground. And then Rotti turns up.
"But he/she-!" As they immediately point at each other...
Grave-Robber's number, "The 21st Century Cure," particularly the moment when he screams out "GRAAAAAAAAAAAAAAAAAAAAAVES!" and is immediately discovered. A very clever fourth wall joke.
When Nathan calls Shilo after she meets Blind Mag while he's out on a repossession, and the victim cries out.
Shilo: Your patients need you. *victim cries out in pain* Dad, who's that?
Nathan: Oh, that? One of my patients, he's sick. *Neck Snap*
Shilo: Will he live?
Nathan: It's looking grim.
Luigi's reaction to Rotti leaving everything to Shilo, going from calling for Nathan's death as he enjoys his popcorn to screeching his displeasure as the popcorn goes flying.
Even funnier, in an earlier right before Amber's face falls off, you can see him stealing the popcorn from another guy. There's just something inexplicably hilarious about Luigi still having the popcorn.
Luigi: (still grinning) WHAAAAAT?! (throws popcorn over his head)
Pavi: All of it?!
Rotti: Oh, yes!
Pavi: Oh, no!
The opening song to the Genetic Opera features a Band Leader who is an undeniable Keet. As the song ends, you can hear the poor guy coughing and gasping for breath over the amount of boundless energy he's got!
Band Leader: Hey hey, hey hey! Hey he-HAUGH ACK!
"Bravi". It's best summarized with the following youtube comment: "A murderer, a rapist, the king of the city and the queen of addiction doingTV commercials."
This deleted scene. Apparently, Graverobber thinks throwing a bale of hay at Amber will distract her enough to let him and Shilo escape. Her expression is priceless, especially since it lands a good two feet from her: she's looking at him like, "Really? Really?"
During "Who Ordered Pizza?", Pavi specifically requests that Nate "handle Mag's face with care" when he kills her. We all know what he means by that...