Girl Days/Funny

The fight with Kodachi in chapter 3.

From chapter 4:

Nabiki held up the paperback. "The Pocket guide to Chinese Amazon Law. I bought it off the Internet."
"Where do they sell something like THAT?!?"
"Amazon.com. Hmm... you think there's a connection?"
Ranma, Akane, and even Kasumi groaned.

Also from chapter 4, the entire Amazon!Ranma and Ranma!Akane sequence.

The entire Anything Goes Martial Arts Baseball Game.

As the Black Rose fumed at this most preposterous of humiliations, a heated argument began between the two team captains. Ranma's captain insisted that the ball had been caught on a pop-fly, so Shampoo was out. Shampoo's captain insisted that Kodachi wasn't on the team, wasn't in the game, and wasn't even in the school, so the ball was live. The umpire was beating her head against a tree and saying something about moving to Australia.

From chapter 14:

"My path is perfectly philosophically sound!"
"Your path includes gorilla suits, obscure dances, and hermaphroditic underwear," replied Nabiki. "What does that have to do with anything?"
"By idiocy I can become wise! The path of success through failure applies to all areas of life except making grilled cheese sandwiches!"
Silence.
Then, Ranma said, "I ain't gonna ask."
"Well, I am," Nabiki said. "Why grilled cheese sandwiches?"
"I like them."

Ranma and Ryoga-chan sniping at each other in chapter 17, while Shampoo and Hilda inexpertly engage in a war of wits.

Chapter 18: Cologne stating that there are no Chinese Inca, because the Chinese Aztecs wiped them all out -- before everyone else in that part of China teamed up to wipe out the Chinese Aztecs.