Giving Blathers a cockroach in Wild World is funny as all hell, thanks to part of his reaction when he opens the conversation when you hand it over to him.
And the fact that if you try to step on the cockroach you gave to the Museum, a VERY sarcastic reminder will appear saying that the cockroach is a "thoughtful donation from the player" and asks the patrons to not step on it. In addition, Blathers will even ask why cockroaches are part of the Museum´s collection.
When Zipper T. Bunny in City Folk mutters how much he hates doing this job.
Dr. Shrunk the Psychiatrist is trying his hand at stand-up comedy in City Folk. Visiting his show earns you an emote, but the real reward it is speaking to the audience members after the show to hear them complain about how abysmally un-funny Shrunk is.
In one commercial for the GameCube version:
Leslie: Nice outfit. Where'd you get that, a garbage dump?
Kelli: Uh... yeah.
Makes it funnier when you realize that they're wearing the same design, just in different colors.
The absolutely brilliant guilty pleasure, in the original GameCube game, of hitting animals with the butterfly net. On the third time, they snap.
And now in the online age, hitting EACH OTHER with a butterfly net. Or a shovel. Or an an axe. Sometimes just hitting each other with tools during online sessions can be a blast, especially if you wear certain accessories.
And in New Leaf, you can buy a squeaky hammer to bop people with.
Even more fun in New Leaf: you can stumble upon your villagers taking a nap on a bench or tree stump. Hitting them with a net while they're asleep is PRICELESS.
Show up to work out of uniform at Tom Nook's store in the GameCube game. On occasion he'll go into a lunatic tirade about kids your age, though the look on his face and the accompanying sound and dialogue box that you see when you enter should be enough to make your sides ache.
Sometimes Resetti will take control of the camera and force it into extreme close-up, making himself fill the whole screen!
And other times, he'll pop up as usual, only to face the wrong direction.
The response to catching a tarantula is pretty funny, mostly because of how blunt it is:
Player: I caught a tarantula! WHAAAA! Destroy it!
If you go to the island with one guy and one girl Kapp'n will assume that the two are married and on their honeymoon.
"Are you two eloping?"
New Leaf now includes a screen capture function and a website for posting them to Facebook, Twitter, and Tumblr directly from the 3DS browser. To say many of the things people have uploaded (particularly on Tumblr) are absolute comedic gold would be a great understatement.
The conversation ending option for Lyle in New Leaf is "You're scaring me."
Lyle mentions to The Mayor that he and Tom Nook were invited over to the Able Sisters' for some bread pudding, and Tom immediately gets flustered, starts sweating and adjusting his tie, and responds "Yes, delicious bread pudding!" With the Ship Tease in City Folk that him and Sable may have once been a thing, it really makes you wonder...
When Shrunk teaches you the Sneezing joke and he starts sneezing repeatedly, he'll mutter under his breath "Maybe it's my human allergies coming back again."
His Disagreement joke. Shrunk starts by pointing out that in some cultures, shaking your head side to side means yes instead of no. After talking a bit about how confident he is in his material, he asks the crowd what they think.
"Hey, hey, you don't need to agree all at once!"
Shrunk's Embarrassment joke in New Leaf is lifted word for word from his mentor Frillard in City Folk. Unfortunately, the joke relied on Frillard's old age to be funny and Shrunk realizes mid-joke that it makes no sense when he tells it. His embarrassment is palpable.
The Reset Surveillance Center. Particularly when a reset happens during your visit.
Resetti: WE GOT A RESET! CODE 64! ... RANGERS, GO!
If you manage to pay off ALL loans for your house in New Leaf (which may take 7.5 million bells), Tom Nook will celebrate your financial successes by singing an anthem, entirely in gibberish. He claims it's an old Nook ancestor song, so it may have been lost in translation.
Saharah's silly dialogue gets amped up in New Leaf.
Saharah: I have many wallpapers for the papering of walls. Many carpets for the petting of cars.