The entire sequence in "Chuck Versus the Truth" with the Truth Serum which will slowly kill them, right after they get a single dose of the antidote.
Casey: You're a good person Chuck, and I respect that, but I've got a job to do now take that before I shove it down your throat! Chuck: Okay. Okay, fine. Fine. I'll do it. Sarah: Thank you. Chuck: I'll pretend to agree to take it and then I'll run like hell to my sister's room and make her take it! Why did I just say that out loud? Sarah: It's the poison. It makes you tell the truth. Casey: You do that and I'll give chase, put a gun to your head and threaten to pull the trigger if you don't. Chuck: Would you really shoot me? Casey: No.
Let's not forget:
Chuck: Casey, your jaw was chiseled by Michelangelo himself.
And when Ellie has been poisoned:
Sarah: Ellie, are you okay? Have you done anything unusual today? Ellie: (beat) ...Words taste like peaches.
Not to mention much of the sequence where they were infected with the serum was set to 'Toxic' by Britney Spears.
Chuck getting drugged in "Chuck Versus the Nemesis." Sarah bends over him in concern:
Casey going undercover at SarahJenny's High School Reunion as the DJ, and dancing to MMMBop by Hanson.
Sarah tells Chuck she has personal plans for the evening in "Chuck Versus the DeLorean." Chuck follows her to find out what's going on. Sarah reveals that she has set up a program designed specifically to sound an alarm on her phone if Chuck decides to stalks her.
Chuck and the villain of week both getting high on nitrous oxide:
Villain: (stopping midway through attacking him with a scalpel) "I don't even remember why I was mad at you!"
Casey in "Chuck Versus the Angel de la Muerte," loopy on anesthesia. He goes from a very gruff, angry, "No! No!" to a giggly, touchy-feely, "Ooooh!" in .02 seconds. And upon awakening, his first words are a smiley, "Heh, hey Chucky..."
In "Chuck Versus Operation Awesome," Chuck discovers exactly how awesome Awesome is not at lying, culminating in:
Ellie:Oh, my God!You were attacked by a BEAR! Chuck: (makes "cut" motions with his hand at his neck, meaning "stop talking") Awesome: YEAH! And I j... I... cut off its head! Chuck: (quietly facepalms) Awesome: Yeah, babe, I...I had to decapitate the bear. ...In self defense! ...In order to survive! I'm just...glad you weren't there to see it. It was really grisly.
In "Chuck Versus the Suitcase," Morgan's presentation about how the new Buy More is too efficiently run, in the form of a monologue as he strolls through the Buy More as he attempts to cause chaos, but the CIA agents hired to run the store as a substation keep fixing everything before anything happens, using all sorts of crazy stuntwork and precise timing. It helps when one of the new Buy More employees is The Man Your Man Could Smell Like.
Kid: I don't wanna be an astronaut anymore, Mommy. I wanna work at the Buy More.
Greta: First you have to finish school, little man.
Jeff & Lester's first scene in season 4 has several within three minutes.
Lester: We are not the boys you are looking for. Morgan: These are not the boys we are lo— Hey, cut it out!
Lester protesting that people have been following them for months after they were accused of blowing up the Buy More, and Casey asking how Lester knows that they weren't just driving behind them.
Lester coming to the assumption that they need Jeff & Lester, so starts demanding a pay rise, the company car & over privileges. Casey promptly shoots him with a tranq gun & Lester drops like a rock, before Casey tries tranqing Jeff... And nothing happens, although Jeff remarks "I think my water just broke", leading to the disgusted Casey firing more tranq darts at Jeff, waiting for Jeff to fall over, before firing more tranq darts. When Jeff remains standing, Morgan just puffs on him & he falls over.
The "Aisle of Terror" in the episode of the same name:
To start with, it was designed by JEFF AND LESTER, using the results of a study Jeff was once in, involving things even the most deranged, fearless lunatics are afraid of. It serves as a Chekhov's Gun which gets turned on Robert Englund, of all people. However, while the most deranged, fearless lunatics may be afraid of everything being shown, for your everyday person it's a list of things that may or may not kinda be disturbing.
Bonus points go to the oh-so terrifying baby in a snail costume and Chuck's high-pitched, half-terrified/half-adoring voice during the sequence.
Chuck: Old people! Black licorice! Man feet! OTTERS!
Chuck's reaction to Casey and Sarah arriving to rescue him after his mother forces him into her car at gunpoint as a means of turning over Englund's character. Not only the words, but Chuck's delivery makes it priceless.
Sarah: Chuck?! How did you get here?
Chuck: My mom dropped me off.
In "Chuck Versus The Fear Of Death," pretty much any scene where Lester and Jeff are stalking Greta, or Greta has to whip out her knife.
In "Chuck Versus the Leftovers," the first time Volkoff discovers Chuck is his right hand woman's son and immediately goes from trying to kill him to wanting to go to Thanksgiving Dinner with him. This just gets better as, a couple of scenes later, Volkoff is playing Charades (and making strange motions, including galloping and dancing), complete with slow motion and "In the Hall of the Mountain King" playing in the background.
How can you not laugh at Volkoff kissing Chuck and Chuck's face?
In "Chuck Versus the Balcony" Sarah getting wind of Chuck's proposal plan, and confronting the hapless Morgan, demanding to know what he knows, and recruiting him for her own purposes.
In "Chuck Versus the Push Mix", Volkoff describing his personal boat, or in his terms, his "floating fortress of fun". It comes equipped with anti-air missiles and an old-fashioned ice cream parlor!
The first time we see Team Bartowski in "Chuck Versus the Seduction Impossible" is a POV shot from baby Clara with everyone standing over her crib making gooey faces. When Clara starts crying, Casey proclaims "I'm outta here" and makes towards the kitchen. There's also his hilarious reaction to mistakenly believing Alex is pregnant, and Chuck, Sarah and Casey desperately realising they need a mission when the rest of the Bartowski family start planning Chuck and Sarah's wedding.
Chuck and Morgan humming and air drumming the Imperial March to get Morgan psyched up before a mission.
Chuck and Morgan kidnap someone and take them to the apartment.
Are we in a bathroom?
No! This is Hell!
Chuck kissing Casey to save him from a virus in "Chuck vs. The Ex".
Casey: I served my country with honor. Please... let me die with dignity!
As well as Chuck's reaction after Jill reveals that doing so was completely pointless and wouldn't have any effect.
Even the RING had it's moments.
Vincent: We detected a computer signal similar to the one Orion used in Hong Kong. We've traced it to a retail store in Burbank, California.
RING Elder: Is it a Buy More?
Vincent: Yes. Would you like me to pick something up for you?
Volkoff just has too many of them.
"I-I know that if you use those tweezers on those rather large hairs in your nostrils it would work wonders. I mean, when was the last time a man expressed...interest in you, hmm? Be honest."
"No, no, no no, no! Please, stop! Stop, stop! I'll tell you everything you want. No, don't! My home address is 17 Tally Place. My dog's name is Kipper. And I had my first sexual experience watching Lawrence of Arabia. I'm not proud of it. I...I came from a broken home."
"Oh cool, a tiny weapons standoff!"
Trying to toss a knife to Chuck on board a plane, but ends up accidentally skewering a mook in the back.
Sarah: Do you know how many skimpy outfits I have had to put on for this team? Did you hear me complain when I had to put on a catsuit, or a seven-inch platform high-heels, or a belly-dancing outfit? Casey: (opens mouth to respond, then realizes:) ...Belly-dancing? (quirks head) Sarah: ...okay, that was private. Look, just put on the banana hammock and stop whining.
Shortly thereafter, Sarah encounters a Primal Scene that...well:
Verbanski: (offscreen) You've been a naughty, naughty colonel. (a spank, followed by Casey grunting, as Sarah looks queasy and rushes out the door) Chuck: (catching up with Sarah) Sarah, what's wrong? Sarah: Everything. It's all wrong.
All of Verbaski's brazen ways of seducing Casey.
"Chuck Versus Bo", the whole scene of Intersect!Morgan partying. It starts off with him arriving at a cabin and annnouncing to everyone there: "WHO WANTS TO PARTY WITH THE FRICKING INTERSECT!"
Every scene involving the Vail Buy More, as we see that there's a group eerily similar to the Burbank Buy Morons.
Casey, in general, once again brings the laughs, especially with his reaction upon having to go to the Vail Buy More to complete the final mission.
Casey: I'm never getting out of this place.
Sarah pointing out that Casey gets shot a lot, with his counter argument that it's not a lot considering how often he's shot at. Chuck, Sarh & Morgan all collectively hum as they take stock of that.
While Jeff and Lester's Big Damn Heroes moment from "Chuck Versus the Bullet Train" is a certifiable Moment Of Awesome, it's got it's hilarious moments too. Particularly when we see Jeff and Lester armed to the teeth with weaponry from Casey's Crown Vic, and threatening the baddie, while Canada's national anthem plays in the background.
While "Chuck Versus Sarah" is more of a dramatic (and quite frankly, dark) episode, something has to be said about Morgan fooling around with an invisibility cloak that he stumbles upon while the Carmichael team infiltrates the DARPA building to destroy the Intersect once and for all.
As to be expected, the Grand Finale "Chuck Versus the Goodbye" has it's moments.
Captain Awesome covering Clara's eyes the moment he realizes Grandma Frost has a gun out.
Devon: Grandma, what did we say about guns around baby Clara?
[Frost lowers her gun]
Frost: That it's a no-no. I'm sorry!
Pretty much any time Frost switches back and forth between her 'super-spy' and 'loving grandmother' personas.