Akira utterly trolling Hanai's attempt to join the Tea-Ceremony club (just because he wants to be on the same club with Yakumo). When he woke up after being knocked out, Hanai saw Akira putting up a message on the wall and looked like she warmed up to him... only for Hanai to realize that the message Akira put was "Hanai is not allowed to join."
In an early episode, Harima mixes up his Love Letter to Tenma and a school resignation letter. Tenma convinces him not to quit school, but his teacher, who got the love letter, is just confused, and says, "Uh, Harima, about this letter...".
Not too long after he tries to give move tickets to Tenma... except she gets pulled away by Nara last-minute and he ends up accidentally asking the teacher. Cut to Harima (a big, tough delinquent) and his teacher enjoying a movie together. The fact that the teacher accepted the invitation is the killer.
While stranded on a cave in a deserted island, Mikoto thought of 4 plans A, B, C, D, with D, being the risky one. She hadn't even said those plans and asked Imadori if he had plans... then he said "D". Mikoto thought Imadori reads her mind perfectly and was warming up to him because plan D is the riskiest... only for Imadori to burst in and saying that Mikoto's breast size has GOT to be D Cup. Cue Megaton Kick.
Later, the girls are discussing how far they managed to swim, since none of them knew how before today. Eri didn't really try, Tenma swam 20 meters, and Mikoto...swam five kilometers.
In the Beach Episode, Harima tries to crawl next to Tenma while she is asleep. Hanai, dreaming of Yakumo, grabs him from behind. They struggle and he wakes up Eri who sees Harima all sweaty and breathing deeply. She kicks him in the face repeatedly.
Eri misunderstanding Tenma and Karasuma's wrestling date as their "first time".
During the camping trip episode, when Harima and Tenma take shelter from a storm in an abandoned school and Tenma starts to sneeze. Harima doesn't want her to catch a cold so he tries thinking of the best way to get her to take off her clothes without sounding like a total pervert. His brilliant idea? Stand up, take off his shirt, and say "Get your clothes off right now," in the creepiest sounding voice possible. Real smooth Harima, real smooth.
Possibly even funnier is that it works perfectly. Tenma is not your usual girl.
Imadori saves Mikoto from during the Kibasen and does a dramatic monologue. Mai tells him to get back in the game and hits him over the head but that causes him to fall down and get eliminated.
At the end of the first episode of the second season, when all the perverted boys from 2-C had gotten files on some of the female students and Itoko, and were anylizing what traits that made them attractive. Then a virus attacks all their computers and erases all the files save one. When they open it, they see what they at first think is cleavage and are drooling all over it when it comes into focus and the "cleavage" turns out to be a candid picture of Harima's butt, with a message from Itoko to stop fooling around and start studying.
During the Wargames it's revealed the girl everyone thought was Eri was really her butler Nakamura in drag.
Harima gets jealous that Tenma is praising Hanai so he reminds the class that Hanai shouted Mikoto's name when she was killed in the survival game.
One of the ideas for the School Play: a Harima/Hanai yaoi fantasy.
The night before the school festival and Eri tries to get close to Harima:
Eri: Hey Hige, I need to ask some questions about the menu. Do you like girls who can cook, yes or no?
Mikoto(comically diving from her hiding spot): That has nothing to do with the menu!
It gets worse.
Eri: Next question... Hige... What kind of hair do you like in a girl?
Mikoto(comically diving from her hiding spot): Now THAT's really got nothing to do with the menu!!!
Akira: That was a very direct one, Eri.
The real CMOF from that part that caused this troper to pause to get some air was that it culminated in Eri having an Imagine Spot where Harima violently rips off his shirt shouting "PIGTAILS! I'M A FIEND!!!"
Through an elaborate series of circumstances the school play (Sleeping Beauty) goes wildly off script after Harima takes a nap in the bed and the actress playing Beauty gets held up. Thanks to some creative improv, they manage to cover, but the crowd is more than a little confused when "Beauty" shows up looking like the resident tough guy... except for Tougou, who thinks that casting a male character — without even dressing him up! — as a beautiful princess is absolutely brilliant art, the "sort of innovation you wouldn't even see in a Broadway play! BRAVO, CLASS 2-C!!". Travis Willingham's delivery in the dub is absolutely hilarious.