Burt holding the return policy of his nice shirt hostage on picture day.
Maw Maw getting fed up of being quarantined in "The Sniffles".
Burt: "There's a predator in your neighborhood. *cough* It's me."
That whole montage, and the scene at the end.
Burt getting freaked out by the computer. On it's own, it's funny. But it's hilarious when you remember that Dillahunt use to play a Terminator. Likewise when he gets snarky and snarks about going back in time to change events.
Burt trying to get Maw Maw to stop smoking. She immediately puts it out—on him.
All three of the possible ads for Howdy's Supermarket in "Baby Monitor"
The spitting contest between Burt and the alpaca in "Don't Vote for this Episode"
Also in that episode, when Barney is convinced his store has a gypsy.
Maw-Maw hears the rest of the cast up in the attic, and starts shooting.
Maw-Maw: "I hear you up there, mongooses!"
Virginia: "We're not mongooses!"
Maw-Maw: "That's just what a mongoose would say!"
Granted, they aren't actually playing those characters, but just the fact that "Baby Monitor" introduces Randy and Joy as a married couple.
A lot of "What Up, Cuz?" Such as the cold open— Jimmy wakes up to get Hope some milk in the middle of the night, and finds Burt hiding in a closet, naked. He's hiding from Maw-Maw, who'd burst in on him and Virginia earlier with her shotgun, thinking he was her late husband Wilfred. When Virginia tries to explain, Maw-Maw snarls "Zip it, harlot!"
To prevent Delilah from knowing Maw-Maw's alive, Jimmy takes to Howdy's to act as a greeter. She says all sorts of unflattering stuff to the customers. She wanders off, and Jimmy finds her in the deli case, leading to this gem of a line from Barney:
Barney: Unless there's some special on aged meats that I don't know about, would you please remove your great-grandmama from the delicase!
And still later, Maw-Maw escapes from Shelley's daycare on a moped and a chase ensues as Maw-Maw in turn ditches the moped, stealing Dancing Dan's skates and boombox, and then Frank and Barney's tandem bike.
The very beginning of "Sabrina Has Money", when Burt is told that the rich guy whose pool he's cleaning is Sabrina's father. He just keeps looking around and stammering in utterly adorable bemusement for about twenty full seconds before the scene cuts away.
Burt yells at a lobster he bought...then immediately apologizes to it.
Everything about the Japanese toilet.
Virginia: Burt...are you jealous of a toilet? Burt: Of course I am!
When Burt shows Hope the picture of her mom in the electric chair, Hope smiles and laughs.
In "Henderson, Nevada Adjacent, Baby!" Sabrina says that Jimmy doesn't seem like the Vegas type.
Jimmy: That's because you only really know Daddy Jimmy. You don't know sex-in-the-back-of-my-van-with-a-serial-killer Jimmy. I used to be a wild man before this little ball and chain came and threw a wet blanket on my party fire. (Hope does something cute.) She is cute, though, isn't she? (devolves into Baby Talk)
Sabrina: You need to party.
Jimmy: Oh, I do.
Also in "Henderson, Nevada Adjacent, Baby!", the montage of Virginia trying to decide whether or not she should go to her terrible cousin's wedding, interspersed with Burt whittling an entire tree branch down to a toothpick.
The unfortunate soul who decided to video chat Maw-Maw. A naked Maw-Maw.
The fact that he later shows up for a date makes it even funnier.
Burt thinking Frank's killed Jimmy, and enters the house to catch Jimmy playing with dolls of himself and Sabrina.
Burt: You can kill him now.
Maw-Maw's series of ideas that would have been amazing 30 years ago. The best is how she comes up with the idea of a 24-hour cable news channel, then immediately dismisses the notion because she thinks it would lead to programs full of pundits just to fill time, which leads to partisan bickering, and thus is a terrible idea.
Opening scene in "Spanks Butt, No Spanks" Jimmy gives Hope her bowl of oatmeal, she throws the spoon at him and giggles. He tells her "Very funny, Hope, but you need your spoon to eat your oatmeal." Hope's response: No! *pushes bowl off table.*
The entire subplot involving Burt and Virginia and the rapist squirrel.
From "The Last Christmas": Burt and the Alpaca, round two.
Maw-Maw vs. Sabrina. Maw-Maw pretty much kicks Sabrina's ass. While in a wheelchair with a broke pelvis after falling off the roof of a car she was car-surfing on.
Burt getting mad at Jimmy and punishing him - by whispering to him exactly what he was going to do to Virginia for their end-of-the-world-sex (whispered because Hope was in the room and Burt didn't want to punish her too). Jimmy throws up immediately afterward.
The entirety of "What Happens at Howdy's Doesn't Stay at Howdy's":
The banana-eating contest.
Maw-Maw: I haven't gotten a speeding ticket since 1962. You're about to find out why.
Maw Maw getting a lap dance from the pizza guy who they thought was a stripper.
Jimmy: Why does that stripper look like Brian, the chubby kid I went to high school with?
Pizza Guy: Hey, Jimmy Chance. Long time.
Maw Maw: Quit staring, Jimmy. You're making this awkward.
The keg is tapped dry, and the party-goers wonder what to do next. Barney realizes he has the keys to a grocery store- next thing you know, Howdy's is invaded by the partiers like a drunken Supermarket Sweep.
Turns out the plot was for Frank to keep Jimmy away from Sabrina by marrying Jimmy while drunk. His lawyer is Wally Phipps, wwho also represents the Chances (total conflict of interest there) and demands a post-nup with bizarre things, such as him taking custody of Jimmy's daughter "what's her name" and immediately renaming her to "She-Frank".
A lot of "Jimmy & Sabrina's Wedding"
Burt and Lucy's father subduing her in the back room, with no one aware of what happened. One of the funniest visual gags was them trying out the shock collar to see if they could hear her scream. As it turns out, while she didn't scream she was one of the statues behind them in the frame.
The wedding cake disaster being treated akin to an oil spill.
In "Sex, Clowns and Videotape", Burt reveals that, in high school, he was voted "Least Likely To Hurt a Fly". The humor is in the fact that Garret Dillahunt is saying this.
Even better is the irony of the scene: Burt mentions this as he tries to get a fly out of the house without killing it. After safely cupping it in his hands, he tosses it outside... directly into the path of a spiderweb, whereupon a spider devours it.