Episode 4: Nagisa accidentally breaks the finger of a fragile statue. Panicking, she tries fixing it, only to break its arm. She tries fixing it for good and seemingly succeeds... only to have the statue look like it's scratching its butt. In a Brick Joke, once she and the school leave at the end of the episode, an art critic appears and praises the butt-scratching statue to be a masterpiece.
Episode 8: The girls have a falling out and, after transforming, are too busy arguing with each other to actually fight the bad guy, or even take much notice of his existence.
An unintentional one in Episode 10 - in the English Dub, the weapons the bank robbers use were edited out. This results in them using Invisible Guns, Yu-Gi-Oh! The Abridged Series style.
In Episode 12, Poisony distracts Nagisa with chocolate while having a mini-Zakenna toss Mepple away from her. When Nagisa opens Mepple's pocket, many Zakennas came out and surround Nagisa, and after a few lacrosse-stick swing, run off... but not after explicitly having themselves form the words "Baka"/"Idiot" right on the air just to taunt Nagisa.
During Episode 15, while Nagisa and Honoka discuss how their enemies might come after them while they're having their family vacations at the same inn, Nagisa opens a door on a cabinet to reveal Poisony inexplicably hiding inside it.
The chalk duster dance in Episode 16.
In the same episode, Cure Black and Cure White are surrounded by the Zakenna that have taken on Yuka's appearance, but they can't just attack since the real Yuka is somewhere among them. Once they've figured out which one is the real Yuka, Cure Black uses a marker to scribble on Yuka's face so they can tell her apart from the Zakenna.
Nagisa spitting pieces of potato chips all over Honoka's face in Episode 21.
During a battle in Episode 28 (the episode of Regine's awakening, to be exact), Cure Black and Cure White find themselves atop an high hill and faced with a veritable army of Zakennas, after having had trouble dispatching five of them. The stress of fighting for so long finally gets at Cure Black, and she looks like she's about to have an Heroic BSOD... but a few seconds later, she begins to speak about how she would like nothing more than have a chocolate parfait, starts lamenting about her homework for the vacation... and finally, it all degenerates into Cure Black angrily ranting and raving at the monsters in front of a bewildered Cure White (who even gets Blank White Eyes for good measure).
Episode 37 has Nagisa and Honoka's hilarious rendition of Romeo and Juliet.
Nagisa and her classmates faking a samba in episode 39 in an attempt to divert their teacher's attention away from the surprise wedding gift they're preparing for her.