Upon working up the courage to face the cockroach everyone else is afraid of, Tomoko squishes it without remorse. And happily goes to clean her shoe as she imagines what her classmates think of her. Good news, they're not ignoring her anymore. Bad news, they now think of her as the weird quiet girl who crushes anything that annoys her, even something that has the rest of the class up and running in the opposite direction. It is both sad, and completely hilarious.
In the spinoff, "It's not my fault my friend is not popular" during one of their earlier meetings Yuu hears Tomoko talking about "getting hard" and is confused by what it could mean. She then reads it up in a book and is confused by the word for the male genital, which she then looks up too and gets more confused. The whole scene makes it look like Yuu is very naive and has no clue about sex. Until the end where it's revealed she knew what it was the whole time but merely knew the vulgar term for it.
Later in the same chapter, Tomoko Googling for NSFW images on her phone in class... and getting caught when she fumbles her phone.
"My mind is so stuck on dicks I can't concentrate at all..."
Of the fraction of girls who have seen a naked guy (penis), Kuroki-san is now well-known to be one of them.
The anime OP. Nothing within the OP itself, but just the fact that a Slice of LifeCringe Comedy gets such a hardcore, heavy metal OP.
The 3rd ED. The lyrics mockingly talk about her "pure heart" and then she goes and pulls an ahegao while throwing up V-signs at 0:45.
The full version of the song makes it abundantly clear that it's about the Walk of Shame. More specifically, the Walk of Shame after doing business with a hooker.
Another moment where she ends up with an ahegao face. During an episode where she reads that sleeping while lying on your stomach can lead to erotic dreams, she tries to do this for several nights but only gets hilarious nightmares instead, leaving her extremely tired in class. Where she, during a test, accidentally falls asleep and has an erotic dream ending the episode/chapter with this face.
Tomoko tends to overreact to small inconveniences with extraordinarily venomous inner monologues which, if said out loud today, would get her suspended.
Kii-chan's expressions of anger are terrifyingly funny.
The ending of chapter 61, where Tomoko's attempt to act as the older cousin and give Kii a serious lecture gets undermined by her Implausible Deniability about the fact that she peed herself when Kii pulled a scary prank on her.
In the spinoff: Tomoko gets a caterpillar on her head. Yuu tries to swipe it off with a broom but she swings too hard and squishes it. Instead of screaming, Tomoko spaces out and imagines she's a samurai, sword in hand.