"I just saw something... black and fluffy..." "I-it was probably just the seaweed ghost!"
The "shower scene" at Ami's beach villa.
Taiga's campaign for student president. "I am going to take over this school, turn your high school memories into a sea of blood, and send you all to the m-m-m-morgue!" And her running mate? Ryuuji.
Ryuuji known in school as the 'Most Pitiful Guy Ever'. Why? In the Festival Episode where he runs for Taiga's sake, you know the one, where her Jerkass father didn't show up, he swore to make it up to Taiga and Minori (with whom he argued with) and tried to win. He tied with Minori, but apparently "didn't get the girl" in the eyes of the student body who don't know the reasons why he wanted to win. This doesn't last too long, though... Because Kitamura gets the title next after attempting to confess to Student Body President Sumire and apparently "getting rejected" (she was to study abroad in America but she actually returned Kitamura's feelings). This does not dishearten Kitamura, who instead makes up a radio school broadcast program about talking about romance problems. This becomes a plot point in the story's latter half...
Another, after the school festival, where he finds a picture of him running in the marathon, looking absolutely like a devil. To his embarrassment, Minori doesn't seem to mind the picture at all. The picture gets a Call Back in the PSP game when Ryuuji gets memory loss; he is actually TERRIFIED of the demon in the picture, who is actually him.
Ryuuji's lampshaded reaction to the Starbucks knock-off: "How is this place not getting sued?"
Kitamura's costume at the Christmas Party. Enough said. It gets a Call Back at the last episode where the class takes a picture with him wearing the same outfit.
The recently-released OVA based off an extra short story, "Ben-to no Gokui", is a mix of Crowning Moment of Heartwarming and Crowning Moment of Funny, hands down. Especially the ending where Ami and Kitamura make Taiga awkwardly "spoon-feed" Ryuuji using her chopsticks like a girlfriend, much to Taiga and Ryuuji's embarrassment and to everyone else's amusement.