Yukari's reaction (and subsequent declaration of minionhood) when Ranma rates the curse she put him under. He rates the curse at a six of ten (for being pretty dangerous, but also pretty easy to cure) and then goes on to state that he won't lose in their prank war. Yukari, realizing that she's nowhere near well equipped to handle the curse that was just lifted, let alone whatever Ranma thinks is an appropriate response, prostrates herself before him, all but chanting "I'm not worthy, I'm not worthy."
The trio stared for several seconds before Keito decided to state the obvious. "This is a Cuban passport and a Spanish-Japanese dictionary."
"Naturally, I've already mastered the basics of the language ahead of time," Jin said smugly. "Me llamo Jin! Como estas?"
Jin's retreat plan also included mandatory acts of cowardess including the fetal position, bidding behind small objects,and clutching security blankets.
During the retreat we also get this excellent line:
"Remember, screaming in terror is encouraged, but not mandatory!"
Ranma killing a twenty-pound spider with a plunger, wearing nothing but a towel. What makes this even more hilarious is that the spider had a health bar.
Kurumu's Imagine Spot where she gives Tsukune a love letter. Her fantasies were like a cheezy romance novel with melodramic crying, Tsukune being buff and charming and carrying her into his room to help 'propagate her species'. But here's the kicker, after throwing Dream Ranma out the room, he had this to say:
"Just for the record, only in your dreams could TSUKUNE Judo-throw ME across a room! Got it?"
Jadeite is usually a humorless jerk but he manages to give us this little gem after he sees Yukari's wand for the first time:
"Before you go any further," Jadeite said suddenly, causing the young witch to freeze, "I just want it on record that I hate your stupid-looking wand," he explained in a completely normal tone of voice. "And by extension, you as well. Carry on."
In Chapter 18 the Youkai Academy bus shows up right when the fight with Kuyo and the old Protection Committee is getting serious. Upon realizing that Ranma is probably on the bus, Kuyo and his subordinates show genuine fear, and even Inner Moka gets a little nervous. A figure stands up in the bus, and Richard walks out, at which point everyone breathes a sigh of relief that it isn't Ranma. Then Ranma kicks him out of the way and walks out and everyone begins swearing violently. Goes to show you that Ranma is considered an in-universeGame Breaker.
Also, at the end of the chapter, Kouma realizes that he was pretty much The Load in this encounter, in spite of usually being one of the groups strongest members.