Big-Lipped Alligator Moment: The "Peter Pan" arc is very bizarre, with a ghost invading the dreams of some of the main characters and trying to trap them in a world of eternal youth. Considering this manga is a Slice of Life with little to no supernatural elements, it's especially jarring.
Die for Our Ship: Kokoro. The fact that he is Hikari's new love interest to sway off yuri fans didn't sit too well for them.
Futaba and Hikari have a lot of this, such as Hikari's habit of standing very close to Futaba, holding hands with her and gazing into her eyes, especially in the first volume. Though Futaba seems to inspire this quite a bit from others as well.
Mato-sensei giving Futaba a foot message comes off this way because of Teko's expression.
In the last scene of the anime, the things Hikari tells Futaba could easily be interpreted as a love confession.
Episode 6 of season 2 has Teko enter a race just to win a kiss from the "prince" Hikari (though she says it's in order to protect her), as well as the two having an intimate prince/princess fantasy while they're in the bath together.
Memetic Mutation: "Hikari is Kermit the Frog!" (due to her exaggerated facial expressions making her resemble a muppet, combined with her green hair)
Platonic Writing, Romantic Reading: The massive amount of subtext Amano put between Hikari and Futaba had many readers believe that this might lead to a romantic payoff. Alas, Amano thoroughly sunk that ship by turning Kokoro into Hikari's male love interest.
Ugly Cute: Cha and Ohime look rather weird for animals that are supposed to be cats, and that is putting it mildly. Some may argue though that this also makes them stupidly adorable.
