Melanie's introduction during the tutorial chapter. She asks if Vayne bought Jess to be naughty, only for it to go over both their heads.
Melanie: I can remember when I used to be so innocent.
Nikki's failure to catch a mouse elicits a snide comment from Sulpher after he shows her up. Remember, only Vayne can understand Sulpher, but she knows it. She ends up running off as a result.
Sulpher: It'll be fine. It's a path everyone goes through to become a full-fledged cat. When she comes back, she'll surely be a splendid cat.
Vayne: Uh, okay... I hope?
Jess' lunch scene.
Jess: Would you like some?
Vayne: It...smells...kinda strange.
Jess: It's good.
Vayne: And it's...purple?
Jess: It's good.
Vayne: Is it...moving?!
Jess: It's good.
Vayne: ...Um...I have to go...
When Vayne makes Salt, Jess complains about it being boring so he gives her the go ahead to create black powder. He only realizes she meant gunpowder when its too late to stop her.
Vayne: ...I did a bad thing.
How'd Jess meet her mana? She caught her with an insect net. Really.
Jess' lie as she tries to explain how she "didn't" experiment by mixing medicine into Nikki's snacks and how she "didn't" panic when she went into shock and made a remedy. Even Vayne points out its a poor cover story.
Vayne: Jess... You're saying it all...
The Vice-Principal goes to check Jess' room after receiving some complaints about insects, sounds, and smells coming from it. One scene later, Jess runs up to Vayne and asks for help.
Jess: The moment she saw my room, she fainted! I should get someone quick, but then they'll see my room... what should I do!?
Flay's first Character Quest has him faking a criminal being in the school, but the actors are so bad and suspicious even Vayne picks up on it. He just goes along with it since they're already at the point where he might as well.
Vayne: This is horrible... And they're obviously students here...
Anna's first part of her Character Quest, the group ask her to stop being so serious and are all standing around her, she somehow thinks she's getting the Freshman Haze and threatens to attack them. Hilarity Ensues as the rest of the team try to catch her to explain that it's just a misunderstanding and they just want her to ease up on the strictness.
Also a moment of Awesome for Flay as he recruits the battle tournament's referee to fight with him while Vayne is temporarily unavailable.
When Roxis finally manages to make a pact with a Mana.
Roxis' mana loves trolling him, which is not helped by the fact that Flay is usually in on the action. The funniest is probably when the group mistakes his fear of Pamela as signs of him having a crush on her and tried to help him with his love life. Pamela heard, went to him, and promptly rejects him for not being her type.
Roxis: Wh...why do I feel so defeated?!
Anna's ending, where Vayne finds out that's she's become quite the combat pragmatist. His shock at the fact she's using her katana (which she coats with poison that can kill a man by its touch) and at the same time hurling bombs is hilarious. His facial expression in the background also sells it.
Vayne: B-but, doesn't that violate your chivalry or bushido or whatever...?
During the Trivia contest, Tony due to losing the first two rounds decides to sabotage things by kidnapping the 108 year old professor, even threatening force but before he can try anything, the professor (previously shown to be nigh incoherent) zooms over and flattens him.
The whole arc could be this due to just how Honor Before Reason Tony is about it before the above scene.
How did Renee kidnap Jess during the Festival? She gave her cake laced with tranquilizer. Nikki points out that she shouldn't take food from strangers, much less someone who was known to go against their group.
After Flay kidnaps Anna, she starts to lecture him on how unclean the workshop is. When Flay looks to the others for help, they flee to leave him to take the brunt of it. Then he runs only for her to give chase.
Vayne: I think that's the first time I've ever seen Flay lose in an argument.
Nikki steals one of Jess' mushrooms and eats it without permission. Jess asks if she cooked it since it was pretty poisonous. Cue her body spazzing out. Lucky for her, it wasn't lethal, but Jess isn't feeling like coughing up an antidote.
Nikki: I'b zorry... I bon't bo it adain zo bwease delp...