Malcolm in the Middle/Funny

Lois wistfully looking on as her whole family brawls with a group of clowns + Kenny Rogers' "You Decorated My Life" = pure distilled hilarity.
Malcolm spends the Cold Opener scraping the most disgusting things off the floor, the garage, and the back of the fridge onto a sandwich. Then he finally sits down to eat it and Reese immediately swoops in to steal it and take the first bite, just as Malcolm planned.
Surreal performance piece—by Dewey and babysitter (played by Bea Arthur)--to the tune of Abba's "Fernando" (ending with the eccentric grandmotherly woman being carted away by paramedics: probably dead, considering the usual level of sadism in the show's humor). Now a Funny Aneurysm Moment thanks to Bea Arthur's death.
On the episode where Lois gets fired from her job at Lucky Aide because the store manager wouldn't take back the bottle of cognac Dewey accidentally shoplifted, Malcolm's family gets some food donations from the neighbors. Lois doesn't like it, commenting on how food donations are always bad. Hal doesn't believe her and asks anyone if they want some olives he found in a can. Lois's response: "Those aren't olives; those are peaches!"
- As a nice little bonus: After Hal is hospitalized, he lets out a huge fart. Malcolm then awkwardly tells his brothers that "The first one to laugh gets their ass kicked".
The episode where Francis has to visit Ida during Christmas. There's a moment where Francis begins to mocks her with a Christmas song from a card he bought her. This causes her to stab him in the leg with a knitting needle.
- And the follow-up where Francis leaves a whole army of these cards in her house after he left, causing her to go insane trying to tear up each one that begins its chime.
The montage when Hal, Dewey, and Reese decided to have fun with the wood chipper. They throw in plushies, watermelons, backpacks, all sorts of stuff, until finally, they walk up with a box of confetti and throw it in the wood chipper. Hal says, "...Obviously, we've run out of ideas."
When Francis gets dumped by his "sweetheart" who he'd ditched military school to be with, he lies down in the woods and cries out in anguish. By itself, it wouldn't be funny, but then Dewey hears his agonized bellowing from the darkness and starts throwing rocks at him, mistaking him for a monster. And then it's freakin' hilarious.
The fourth season episode "Boys at the Ranch", where Malcolm, Reese, and Francis are setting off fireworks at night. As the fireworks wind down, Reese asks "How can you tell which one's the Komodo 3000?" His question is answered a second later with a fireworks explosion so bright, it turns night into day for about five seconds. See the full clip here.

Francis (deafly yelling): "DID THEY TELL YOU WHEN OUR VISION WOULD COME BACK?"
Reese (also yelling): "BOX SAID TWO DAYS!"
(beat)

Francis: "TOTALLY WORTH IT!"

When Lois has just given birth, she tries losing her baby weight. But Hal has just realised that he's a Fat Admirer, so he sabotages her diet attempts and secretly fattens her up instead. He stirs chocolate syrup into her tea and, when she buys celery, fries it in bacon grease. An hour later, she sits at the kitchen table telling him about how she's actually gained despite her diet, then stops and looks at the celery. Beat. Then she keeps chewing, telling him "My hormones are so screwed up! This celery tastes like bacon!"
Malcolm comes to the couch with two sodas, and Reese goes through a I Know You Know I Know trying to figure out which one he shook up. Eventually he decides to just get a soda from the fridge...which promptly explodes on him.
Hal and some other dads are in a class for bonding with their babies. After the instructor leaves they start having competitions involving the babies, which can spit up more, which can sit up on its own the longest, etc. eventually getting to them playing shuffleboard with the babies as the disks. Lois and the rest of the family walk in at the exact time Hal is doing this. He wins, and starts gloating. One of the kids then asks Lois why she isn't yelling at him yet. Her response:

Lois: See that goofy look on his face? I want to remember that look. We're not gonna be seeing it for a long time.

Reese cooks for Thanksgiving for the first time. He grabs the turkey barehanded before it got overcooked and tells Piama to get those pot holders off the table.
When Reese is being pushed to the ground by the cops, in the background, you can see the Hamster Ball roll past.
Francis comes home after dropping out of military school, assuming that his parents will be calmly okay with it since they've had a week to absorb the news. Cue Hal chasing Francis down the street in a murderous rage.
Stevie has some great ones, but one of the best comes in an opening bit where Malcolm threatens him with a beating if he laughs at Malcolm's Shakespeare recital. Stevie's response?

"Bring it, >GASP< Homeo"

From 'Stilts'

Reese: Francis, you've gotta help me! I don't wanna take drugs anymore!
Francis: Okay Reese, I want you to tell me, very specifically, what kind of drugs did you take?
Reese: All of them!!
Francis: Dude, didn't you learn anything from the time my friends babysat you and Richie tried to dry you off in the oven?

Hal: I accidentally spent $800 on phone sex!
Lois: I was doing my makeup in the rear view mirror, and I ran over your golf clubs!
Hal: I burned a hole in your favourite dress!
Lois: You didn't get that promotion because I called your boss a fat-ass at the Christmas party!
Hal: I lost my wedding ring three years ago! This is part of a lawnmower!
Lois: Your Aunt Lucy isn't angry with you. She's dead, I just forgot to tell you!

In the episode Pearl Harbour, it takes Jessica a long to time to convince Malcolm that Reese might be gay (It Makes Sense in Context). When she needs to do the same to Reese...

Jessica: I didn't do it for myself, I did it for your brother.
Reese: Malcolm's gay? I knew it!