Ichika making all the girls Face Fault with his introduction. Capped off with Chifuyu pulling off a Dope Slap on him.
Hell, Ichika's monologues are pretty hilarious just by themselves.
Ichika's explanation as to how he beat an instructor during the exam. The dry, "I don't know what the hell happened" voice he uses is what makes it funny.
Ichika: Well, I don't know if I'd call it a "defeat"... but when the instructor charged me, I dodged, she smashed into the wall, and "Ka-boom".
Rin's look of rage upon discovering that Ichika and Houki are sharing a room.
Rin: But what does being childhood friends have to do with taking a shower?!
Ichika: Oh that. That's because Houki and I are sharing a room right now.
Later in the same episode, when Rin is trying to switch rooms with Houki, Houki snaps when Rin seems to ignore her, and prepares to strike her with her Kendo sparring blade. Ichika, upon realising this, cries "Not in the house!". It's probably a poor word choice in the translation to English, but it makes Ichika sounds like he's implying 'I really don't care if my first childhood friend attacks my second childhood friend, but if they do it in our room, they might break something!'
Houki punching Ichika in the face, and kicking him in the gut so hard it lifts him off the ground for saying he'd make good on his promise to go out with her...on a shopping date.
Has a equally hilarious and now memetic name: the Houki Pouki.*
A play on the children's song "Hokey Pokey".
And Char's observation immediately thereafter: "Sometimes it makes me think you are doing it on purpose."
The day following Laura's VT System incident:
Put the moment in context at the end of episode 8 and it's even better: start with Charlotte's (re)introduction to the class. As everyone takes in the implications ("Hey, weren't the boys in the big bath last night?"), in comes Rin through the classroom wall in her IS, firing her Impact Cannons on Ichika at point-blank range, but only for Laura to block the blow...
She then turns around, grabs and picks up Ichika while still in full IS mode, AND steals a (very long and very open-mouthed) kiss, then later declaring him as her wife.
Cue dropping jaws from the rest of the class, then to Ichika who took a while digesting what just happened...
Becomes funnier in the anime, where Ichika initially sighs, as if to say 'oh great, more girl drama', only to follow it up with 'HHHHUUUUUUUUUUUUUUUUUUHHHHHH!!!!!' and a look somewhere between shock and horror as his brain fully registers what Laura just said.
Ichika reciting pi just to distract himself from seeing Charlotte strip to change clothes.
And apparently Ichika's type is, I dunno, his sister, probably?
This exchange in ep 10
The Girls:You're handing him over to us?!
Chifuyu: As if!
May count as some sort of 'Fridge Funny', but Chifuyu tells the girls that they'll have to go all out to claim Ichika, then in Episode 13/the OVA we find she has discovered that her choice of words has led the girls to think of her as yet another rival for Ichika's affections. When you think about it, that means that at some point Chifuyu must have been thinking back to that moment, and suddenly realised "Oh ***, those girls think I desire my baby Brother!"
When Ichika was about to kissHouki, he gets poked in the head with one of Cecilia's Attack Drones, that nearly blows his head off, followed by the rest of the harem chasing them down in pure jealously.
Special mention to Charlotte and Laura; the former for breaking out of her Nice Girl image; the latter for this:
Laura: You're not paying enough attention to being my wife!
Also worth mentioning that one of them suggested using Ichika as target practice.
In volume 7, Laura throwing a knife at a picture with Ichika's face on it, only to realize that it was a rare photo of him that was worth 200,000 yen with negatives that she burned. Cue:
The Cinderella play during the school festival.
Cecilia's cooking skills. So much so that everyone tried to dissuade her from making a dish in the OVA. It didn't stop her from using one of Blue Tears' Attack Drones on a metal pot, though.
To give an indication, from what we see of her dish, it's a glowing molten sludge containing meatballs, to which she adds what appears to be tomato ketchup and tabasco sauce. And by 'adding' we mean empty the entire bottle(s) into the pot.
Made funnier by the fact that when using said attack drone caused the pot's contents to explode, her response is a completely calm "Oh drat it" which makes it clear that this is a frequent result of her 'famous IS cooking'.