These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Kyasin's Rousing Speech to the Wulong people in The Winter Solstice, which involves destroying an ancient tree and a beautiful painting, and demanding that they prove themselves to be the guardians of the forest.
Sakodi dueling a powerful spirit and winning in The Winter Solstice.
Fan Nickname: Before they were given original names by the author, Revised!Katara was dubbed 'Katlara' by readers, while Revised!Aang was known as Apathetic Aang by detractors.
The series as a whole has been dubbed 'A Song of Icebending and Firebending.'
To Zotu, his father's decision to sacrifice multiple entire platoons to distract the Earth Kingdom military while one of their cities was overrun, would be this. Horrifically burning half of his face off afterwards did not help his father's cause.
Kyasin has a few candidates of her own, though Word of God is that she ultimately will not commit what would have been hers, officially: coldly executing Yon Rha after confronting him on her mother's death. The other candidates would be executing Rin/The Mechanist in Book One, murdering Dai Li officers that were just doing their jobs in Book Two, and threatening to kill Ain in Book Three.
The Enforcers, of Chapter Six: The brutal murder of Xin Fu on the grounds of gambling debts certainly counts.
Pick any moment from Hook's backstory section in Chapter Eight.
Jiao's would have been compromising his honor by informing Aizo of his son's actions. Unfortunately, not doing so was his MEH for a subordinate officer, which ultimately leads to Aizo discovering Zotu's treachery anyway.
In-universe, Jeong Jeong regards his as being the murder of one of his former comrades-in-arms, Jiao.