From the Carwash episode, Tommy impersonates his grandpa while foam fills up the car, by putting bubbles on his face. It later becomes a heartwarming moment when you realise that Tommy's impersonation helps Chuckie get over his fear of the carwash.
Another moment at the beginning of the same episode where the camera cuts back and forth between Chuckie's interpretation of events at the carwash and Chas's.
From "I Remember Melville":
Tommy: I know! We'll get Chuckie a new bug!
Phil: Hey, if we find two bugs, can I eat the other one?
From the episode "The Seven Voyages of Cynthia," in which Tommy and Chuckie lose Angelica's doll, but are afraid to tell her:
Tommy: Hey, Angelica... uh... we got something to tell ya...
Angelica: What is it?!
Tommy: Uh... it's about Cynthia...
Angelica: Oh, Tommy! Do you know where she is?!
Angelica: Cuz if I find out who took her, I'll mash em, and crash em, and smash em into a million zillion blobs of applesauce!!!
Tommy and Chuckie: *gulp*
And then, after agreeing to help her look for Cynthia, Tommy and Chuckie pretend to search around Tommy's backyard:
Chuckie: Tommy, what are we doin' in this bush? We know Cynthia's not in here...
Tommy: Well... I guess we could tell Angelica what really happened...
Chuckie: I don't know, Tommy. You wanna end up a blob of applesauce?!
On representing herself in court ("Pickles vs. Pickles"):
Angelica: Your highness, I'd like to dismiss my lawyer for gross incontinence.
Didi: Stu, you'll never guess who's coming to dinner!
Stu: Sidney Poitier?
Chas' recap of Chuckie's first visit to the barber: "And after he smeared the industrial strength cologne and got into the barrel of hair, he knocked over a tub of lather, skidded into a shelf of shampoo, and snapped a cardboard cut-out of Crew Cut the Clown right in half."
Arguably, Chuckie's mangled retelling of the same tale to the other babies was even funnier.
Grandpa and Stu's conversation about appropriate camp stories is hilarious, because of the reversal of expectations:
Stu: Say, I hope you're not reading the kids anything too scary, pop. Lou: Well, that all depends. It might be scary if you're thirty-five years old and you suddenly realize that you've never really lived! Stu: ...Look, pop, are you sure about this whole camping experiment? Lou: Stu, just because you had one bad eensy-weensy experience in the woods doesn't mean you have to wreck the great outdoors for everyone. Stu: Teensy weensy? I was lost for three days! Lou: Stu, that was over a year ago. Isn't it about time you put it behind ya?
And this follow-up conversation a bit later:
Didi: Stu, this isn't Manitoba, it's our backyard. The kids'll be fine. Just forget about them, and soon it will be morning, and we can all go on with our lives!
Stu: Yeah, I guess you're right. Good night.
(Light goes off, then comes back on)
Stu: What if there's a flash flood?
Didi: Stu, go to sleep.
When Tommy spends the weekend at Chuckie's house. After Tommy wakes him up over and over again to say something innocuous like "I'm glad I'm staying at your house," Chuckie finally has enough:
Tommy: Hey, Chuckie... Chuckie: WHAT?! Tommy, what?! I'm trying to sleep! Tommy: Oh, I was just thinking about green jello. Chuckie: Green jello? Tommy: Yeah, how do they do it? Chuckie: Do what? Tommy: Make it green. Chuckie: I don't know, Tommy. Just go to sleep! (They do, but then Chuckie's eyes shoot open.) Chuckie:(whispering, frightened) How do they make it green?
Grandpa: Remember what happened the last time you boys put on a show? Stu: Oh, come on, pop, my arm healed, and Drew sees almost perfectly out of that eye.
The scene where Stu and Drew argue about their childhoods during the puppet show, which descends into a family therapy session.
Stu: That was my bike! I earned it with my paper route! Drew: It was still usable! I only bent the handlebars a little! And that was on account of what you did to my skateboard! Stu: SKATEBOARD!? SKATEBOOOARD!!! Didi: Okay, let's agree to disagree. Stu, you shouldn't have wrecked Drew's skateboard. Drew, you shouldn't have bent Stu's handlebars. Boris: What's the matter with you, Didi? Let the boys argue.
To add to the humor, keep in mind both of them are still moving and communicating with their hand puppets while knelled down inside the prop theater while this whole argument takes place.
Grandpa killing Tommy's pet tarantula in "Spike Runs Away." So what's for dinner?
Stu buys two gerbils, and the kids let them loose in the basement. Several weeks later, Tommy and Chuckie open the basement door.
Chuckie: Look, Tommy! The floor's movin'!
While they're staring at the basement floor, Stu finds them and sees the "moving floor" and immediately yells, "Didi! The gerbils have reproduced!"
Even before that scene is a great joke, when Didi is annoyed that the gerbils keep leaving their little "presents" all over the house. Tommy and Chuckie exclaim, "Presents?" Smash cut to a close-up of gerbil poop.
Tommy: Hey! This isn't a present! It's gerdil poop!
Lou and Stu arguing with each other:
Lou: Why do you always lose your keys, dag-nabbit?!
Stu: Why do you always talk like a prospector when you're aggravated, "con-flabbit?"
The entirety of "Angelica Orders Out", where Angelica gets hold of Stu's latest invention, a voice-changing gadget that makes her sound exactly like her mother. She uses it to call a restaurant and order every single dessert they have for delivery. When the delivery boy shows up, she grabs a picture of Didi, and speaks to the delivery boy through the mail slot.
Angelica: Just leave the bags by the door and go away.
Delivery boy: Uh... what?
We see a picture of Didi peeking through the mail slot in the door
Angelica: Down here! Just leave the bags by the door.
Delivery boy: Uh... okay. Thank you for calling Zippy's Snappy Home Delivery.
Angelica's supposedly fake Flashback in "No More Cookies". In the first part, it seems like it's going to be a Heartwarming Moment, with Angelica's mom and dad telling her to say "mommy" or "daddy", respectively. Her first word?
It gets even funnier in a later scene, where we see her taking her first steps. Her parents go crazy trying to save the magical moment for posterity...then they realize that she's just trying to get a cookie on the table.
One of the best scenes is Grandpa naming off past experiences Stu's had with fixing things, all ending in some form of disaster. The best one is obvious.
Grandpa: This one I STILL don't understand! October 3: Change the Refrigerator Lightbulb: 4 broken fingers and a case of pink eye?
The Pirate Episode:
Tommy: REAL PIRATES LIKE SAND IN THEIR SHOES!
The entirety of "Regarding Stuie", where Stu hits his head and thinks he's a baby.
Tommy & Chuckie's Wild West style showdown with the "Junkfood Kid". She smacks Chuckie across the cheek with a chocolate bar, leaving an imprint ("I've been branded!") Tommy bends over to help him up, and she shoves a popsicle down the back of his diaper.
YOWCH!! It's cold!!
Chuckie's reaction when Tommy begins planning The Quest of the Week in "Let There Be Light":
Chuckie:(from under his blanket) No way, I'm not goin'! Not this time! This isn't just regular-plain-old scary, Tommy. This is THE DARK! There's no light at all, not even a night light! Forget it, Tommy. I'm. Stayin'. Right. Here.
The Garage Sale episode. After the babies have sold everything inside the house, and when Stu is brooding about it, Didi comes along with a little speech about how they still have each other and losing all their material goods can bring them closer. Stu's response?
Stu: Put a sock in it, Deed.
I'M NOT TOMMY!
I'm not Stu!! BWAHAHAHAHAHAHA!!!
This exchange from "Angelica in Love":
Angelica: I'm playing the most dangerous game of all.
In "Piggy's Pizza Palace": Tommy giving commands to the dog suit in Yiddish.
From "Naked Tommy", this exchange between Betty and Didi when they find the babies naked.
Betty: Sweet goon von goolagon! What's going on here?! Philly, Lilly, you're nudists!
Didi: Betty! I'm surprised at you, they're just babies, Lipschitz says...
Betty: Never mind that hippie Lipschitz! I don't know what kind of baby colony you're running, Deed, but it's time to face facts! The sixties are over and we lost, so get with the program, alright?
The end of the episode where Tommy is afraid he's turning into a monster. Betty's brother stops by and says "Big sisters are monsters". Tommy then says to Phil "Isn't Lil a teeny bit older than you". Lil turns around with candy canes for fangs and Phil runs away in terror.
The end of the episode where Angelica tries to convince Phil and Lil that either of them is the unfavourite. She walks in on Charlotte and Betty talking about sweaters.
Charlotte: My favourite will always be Angora.
Angelica: (terrified) Who's Angora!?
The "Vacation" episode where they go to Las Vegas and Angelica gets up on "stage" in the snack bar and starts singing her own song "Angelica the Beautiful". Then when the mothers leave the Circus Giganticus hotel and see Angelica performing hew own rendition of "Vacation" on the big TV outside. Their reactions are priceless. This scene also counts as a CMOA.
Charlotte: (on the phone to Jonathan) What? Not you Jonathan; you know I wouldn't call one of my employees sweetie. At least, not since the Clarence Thomas hearings.
Which was part of Angelica setting off one hell of a car alarm in the parking garage with a voice saying "Stand back! You are too close to the vehicle!" to which Angelica responds, "Hey Mommy, neat! A talking car!" Then when the main (and loud) alarm starts up, all Angelica can say is "Cool!"
While we're on Charlotte/Jonathan, there's this bit:
Charlotte: (To the kids) Say bye-bye to mommy!
Jonathan: (Talking to Charlotte on the phone) Bye-bye, mommy!
Charlotte: Not you.
From the episode where Angelica learned a swear word, just the end where she casually says, "She thinks we're all, little..." and then her parents scream to censor the word out. It also offers as a bit of a funny moment considering several kids actually would have done that in her shoes because they didn't know the consequences!
YMMV of course but from the same episode the restaurant owner constantly calling her "Angie" always made this troper chuckle.
At the end of "Angelica the Magnificent," Tommy picks up Angelica's supposedly magic wand. He points it at the shed the dads spent all episode putting together and utters a "magic" word. The shed promptly collapses (though due to shaky workmanship), but the look on Tommy's face and the way he slowly lowers his arms are priceless.
In "Kid TV", Phil and Lil make fun of a soap opera. Angelica doesn't quite understand soap operas and comes on wearing a viking outfit and singing about how if it was an opera, they had to sing.
Chuckie's attempt at telling the most un-scary "scary story" he can think of so he won't scare himself:
Chuckie: So, um...the boy opened the door, and...he finded the most beautifulest room with lots of flowers and big fluffy pillows and bowls filled to the top with yummy candy! So the haunted house wasn't haunted after all, and the scaredy boy wasn't scared no more. The End! Angelica: What?! You can't end it like that! That wasn't even scary! A scary story doesn't got flowers and pillows and candy! Now tell it right! Or I'll start telling the story again! Chuckie: So, then, um...the boy, uh, opened the door...and the room was kinda dark. And there was pillows, but they was hard and lumpy. And the candy was yucky.
In the movie Dil dirties his diaper and Tommy goes "It looks like we'll have to change his diaper" and Phil goes "What do you mean we?"
In "Stu-Maker's Elves", Chuckie bounces up and down on a mattress and has fun but then bounces so much that the mattress closes leaving his head sticking out. That visual and his scream of "TOMMYYYYYYYYYYYYYYYYY!" are priceless.