Sena casually saying "Kneel so I can step on you".
What sells it is her treating this like a reward.
The Neighbor's Club's forays into the video game world. Especially the second one, where they manage to screw over one another even without PvP.
Rika's delivery of the H-Doujinshi Mecha X Mecha. Made even funnier with voice delivery.
Rika is THIS in general, due to being so honest about her perversion.
Rika: I think I can go for anything, as long as it's erotic.
The whole cellphone exchange between Yozora and Kodaka.
Episode 10... the entire episode 10.
In particular, after Yozora's scary story. Kodaka and Yukimura weren't scared, but most of the girls were. And each has to go to the bathroom in turn, but are too afraid to go alone, so they enlist Kodaka. First comes Sena, then Kobato. By the time it gets to Maria, he's caught on. So when Rika comes in...
Kodaka: Let me guess. Bathroom? Rika: Bathroom? I'm here to sleep with you. [camera cuts to hallway, showing Rika being thrown out of the boys' room] Kodaka:Get Out.
Maria: It's true that I have never done it before, but I could have secks whenever I want! If you want, I can do it with onii-chan (Kodaka) right now!
The company that Rika works for is called Large Hard.
In the first episode, Yozora is caught talking with her "air friend". What instrument does she play during the end credits? Air guitar!
In the OVA episode, where the characters take turns writing the same story, they each do things which either glamorize themselves, does Wish Fulfillment, or else insults their rival, such as Maria writing about Kobato smelling like poop and turning into ash when she gets purified at a church. Yozora writes about Sena getting gang-raped by ugly monsters and making pig noises note In case anyone's worried about an actual rape being depicted, Sena actually just appears to be sat on by one of the fat monsters, and Sena returns the favor by making Yozora the Big Bad and extremely stupid and fat, while she Ret Cons Yozora's depiction of her as simply a test and appears as a goddess.
During Rika's explanation on how friends (and men) can kiss anytime because it's human nature, pay attention to Yukimura in the back. Where's that heavy breathing and moaning coming from? ...Yukimura, where are your hands?
Episode 2 of the second season has the Yaoi vs. Galge debate. Sena doesn't understand how Yozora can approve of an all ages Yaoi anime when she refers to her gal games as trash and has Yozora recite lines from the yaoi anime they watched. To her dismay, Yozora recites them perfectly and then forces Sena to once again recite lines from her game to prove it isn't shameful trash. This time, Sena actually reads them. Cut to Yozora blushing and apologizing, Yukimura calling her a pervert and Rika saying that even THAT was too much for her. Sena runs off, crying AGAIN and we get this little gem:
Sena: YOZORA'S A PERVERTED HOMO GAME LOVING MANIAC!
The first episode of the second season has Sena looking up at her stalker collage of Yozora's pictures and smelling a wig Yozora wore to make fun of her, talking about how she plans to get revenge of Yozora...and then you notice her hand between her legs, her face all flustered and her eyes sparkling.
When the cast gets on the Black Dragon roller coaster, Sena, Yozora, and Kobato are all confident because it was slowly taxiing them up the ramp. Then a sense of dread sets in as they get higher. Finally, the drop comes and everybody freaks out. "Fuck."
Instead of screaming, Yukimura starts chanting a sutra (apparently this one) in an impassible tone of voice that Kodaka can hear just behind his head, which scares him way more than the ride itself.
Don't forget Rika's orgasm. "PASS AT THE SPEED OF LIGHT AND EJACULATE!"
Just Rika by herself. The number of things she says and does are enough to fill this page up completely.
Both times Kodaka is invited over to Sena's house. OH. MY. GOD.
Lets start with Sena's father's embarrassment at his name "Pegasus" to the point of blushing.
Stella's "Please don't stare at me Kodaka, I might get pregnant", delivered in perfect deadpan.
Pegasus' speech getting progressively more and more slurred as he drinks more wine, and even repeating the same thing. All ending with him falling face flat onto the table, getting up, walking to his bed, and finally sleeping.
After Kodaka sees Sena naked she calls him a number of things, cue Stella to come in and add "Noooo Kodaka you pervert" in her usual stoic voice.
To top things off, the second visit in Season 2 Stella asks Kodaka how things are progressing he says "I'm getting here." Stella, clearly not understanding what he meant says, "I see. Please use this if you like" and hands him a Condom this is made even more amazing by Stella's exiting line "Please enjoy yourselves" as Kodaka shakes from surprise.
One of the classic "something is weird" indicators of anime getting inverted: mother and child walking around and giving commentary. Like this:
Mother: Oh look over there, a weirdo! Son: Mom! Don't point at people!