Katara accidentally groped Zuko and bemoans her fate:
Before I had been Katara—his person who was nice, comforting and huggable.Now I was Katara—the person who just wanted to grab some arse. Katara— the arse grabber instead of Katara— the nice hugger.
Katara and the commonsense stick.
On Katara's birthday, she gets to order people around with her "birthday powers," using them for various silly purposes. Sokka, in particular often gets ordered to do pushups when he does something stupid, when he complains, or when Katara feels like it.
Similarly, when Katara gets bitten by the scorpidillo and is given a bell to summon her friends, she (ab)uses it quite frequently to get them to do what she wants. At one point, she gets Sokka to do pushups again, and one section later, she simply writes, "I didn't say stop Sokka."
The exceptionally immature taunting letter that Zhao wrote to Zuko after capturing Aang.
Dear Zuko, Ha ha ha. I caught the Avatar. You idiot. Ha ha ha. Sucks to be you! Ha ha ha. Zhao.