Rei's entire match against Matsunaga in episode 9. All of it. You know it's funny when a serious flashback Rei has involving Kyouko in it gets used comedically before Rei decides to go ahead and swiftly beat the old guy in the game they were having because Rei thought it was way too painful and awkward for him to continue playing against him, noting internally that it would be difficult to lose on purpose even if he wanted to!
Rei's Spit Take after he sees Nikaidou on TV. There's also Hina and Momo's reactions to seeing Rei on TV, just seconds after Rei tried to slowly slip away after realizing that he's in that broadcast too.
And then there's Rei's uncharacteristic rant against Nikaidou after the latter started grilling on his playstyle in his commentary during Rei's broadcasted match.
A chapter after that, we have Rei's jealousy at Nikaidou for being a better shogi teacher to Hina and Momo after Nikaidou gives out this beginners-friendly how to play shogi book meant for kids to the sisters. There's also Rei's reaction when he realizes that Nikaidou was the one who wrote, illustrated, and published the book.
Everything about the After School Burners Club in Chapter 32 (Episode 16 in the anime). They immediately call Rei a nice guy after he accidentally bumped into chemicals on the table and created a new scent for their soap. Their leader is a first year student who has a mustache.
Kyouko referring to Akari as an "old woman" before correcting herself at the last minute following her chance meeting with the Kawamoto sisters earlier that day and asking Rei about them once they got home.
In the same scene, thinking Rei has a thing for one of the sisters, Kyouko, for one reason or another, brings up Momo, and, seemingly appalled at the thought, begins to label Rei as a pervert!
And before all this, Kyouko eating almost all of the bento Hina and her sisters made for Rei and making nitty-gritty comments about the food with each bite she takes.
After the first day of Shimada's workshop, Rei and Nikaidou continue to bicker about their Shogi moves all the way home without stopping... until they saw a bird nearby dived under the river and never came back up, upon which they dartedto nearest bookstore to find out if it's dying.
During the matches in Kyoto, Rei is commentating with a very energetic A-Class veteran and is so overwhelmed that he thinks if Shimada had to play with people like that day by day for years and only got stomachaches because of the nerves, it makes Shimada a monster in his own way because the pressure is just too much for Rei.
Hina and Akari's mortified expressions when Momo suggested using gum as a filling for a new sweet their grandfather wanted to make. On the other hand, while those two were less than satisfied at the suggestion, Someji reacts with proud Manly Tears at Momo.
Akari's imagine spot of laser-firing grandpa-zilla being unleashed on parents of the bullies that picked on Hina in Episode 29.
After a match against Subaru Hachiya, a very noisy player, Smith and the Club's chairman who were playing next to Kiriyama scolded him for not bagging the damn guy sooner and went for the move that made Hachiya even more pissed, as if it can easily be done.
This from Episode 29 end card screen in the anime, after Hachiya dragged Kiriyama to a post-match review in a family restaurant.
Hachiya: "Kiriyama, you're not thinking of going home soon aren't you?"
Kiriyama: "Excuse me! One more parfait!"
Hayashida-sensei in Chapter 60 threatening to go ham on Hina's homeroom teacher who subject Hina to victim-blaming after hearing updates of the story. It's Kiriyama that has to stop him this time.