Gone Horribly Wrong: To say that Hawk Moth didn't intend on his latest akuma causing a city-wide, magically induced orgy would be putting it lightly. The fact that it made him rape Nathalie and his son rape his classmate just makes it sting more.
My God, What Have I Done?: Pretty much everyone in the chapter has this reaction when the brainwashing wears off. Gabriel for causing it, Adrien, Alya, Nino and Marinette for what they went through while under it.
Not Wanting Kids Is Weird: The Inciting Incident that akumatized Mabel LaCrux into Fairy Grandmother is when her daughter told her that she doesn't intend on having kids.