The entire episode is hilarious for that matter, but a more precise example would be *Bosspecter's Epic Face* when he realizes they are trapped in the warehouse.
J-son sensei's attempts on his marriage interview are hiliarious with his nervous actions playing out like a horror movie.
Samurai and Pudding's Real Life meet-up, starting from Switch's schemed set-up. Having the two completely look right past each other up until their awkwardly shocked/embarassed faces at the realization of just who they've emailing the entire time is hilarious. Then they start acting out the usual scenario.
Chuuma's concoctions are practically a recipe for humor:
Bossun's expressions getting mixed up.
The entire shenanigan with the invibility potion. It even breaks Switch's usual stoic face. Then he goes on an extended rant afterwards.
Himeko trying her hardest to ask Bossun out on a date in episode 43, and acting shocked when it actually works.
Basically, you couldn't believe that Tsubaki is WAY too clueless, gullible, and spaced out. Admittingly, he is way too Hot-Blooded when it is about his duty as the Vicepresident/President of the Student Council. But come ON:
When he is dressed as a girl, alongside Bossun and Switch (Katou is anime only, though) for the first time just to make Usami more comfortable around men... he is just... acting way too reserved or even distanced meanwhile the others act a little bit more in character.
His sense of fashion with his own T-shirts.
Not knowing about common known technologies as videogames (until Bossun invites him to try one) ot what is an USB (confusing it with a pencil lead, for god's sake).
And he is so easy to fool (especially when he lost his contacts).
How about being targeted by 30 or so gun-wielding mafia (while Katou was practically all over him to deflect the bullets) and he doesn't even notice anything strange
Everything that is related to Remi. Her family is even more clumsy than her (with exception of her brother) too!
Special mention is that some of the incidents caused by Chuuma's experiments are even her fault.
Agata's way of thinking about the whole Love Dodecahedron theory about her sister Saaya. That just the part of 'Saaya is in love of Bossun (that he didn't even think of, he thought it was Saaya's feelings about Tsubaki)' was true.
Sket-dan (along with Saaya and Michiru) devices a complex scenario to clear up the misunderstandings so Agata could focus on his second entrance exams, only to make things worse. Thankfully he managed to clear it before going for his exam and even managed to get perfect score
The whole School Trip Rhapsody arc. And the whole shenanigans that happened in there... mentioning one is not fair: