So, the Big Bad has kicked many dogs, Jumped Off The Slippery Slope, crossed the Moral Event Horizon a few times over, and has truly become a Complete Monster. And yet, this character is still given remarkable leeway by the universe and The Hero, who may be convinced that even a Complete Monster is redeemable, although the audience can see that it will never happen. And then, this character does something simple and minor. He decides to Kick the Dog just one more time, choosing a target that The Hero in some way considers sacrosanct, a target that triggers The Hero's Berserk Button. Suddenly, all bets are off for The Hero, who decides that this Big Bad must be stopped at all costs. It could be as atrocious as threatening the family of The Hero, or as innocuous as putting down The Hero's choice of clothing. Whatever it may be, the balance shifts, and it becomes clear that the Big Bad Complete Monster is about to die or otherwise be neutralised as a result. Occasionally, The Hero isn't the one who actually dispatches the villain. However, The Hero will still be quite happy with the result. Compare with the Self-Disposing Villain, especially when Hoist by His Own Petard. Contrast with Karmic Death, where it is a major, Moral Event Horizon type act that brings about the villain's death. If the villain's Last Dog is The Hero, may take the form of a Backstab Backfire. As this is typically a Death Trope, expect spoilers.
Examples:Anime and Manga:
- In Dragon Ball Z, Frieza does all sorts of unpleasant things to various good guys, good species, and good planets, establishing him unequivocally as an irredeemable villain. Goku finally defeats him by chopping him in half with his own energy disk, then feels pity and gives Frieza a little of his own energy so he can get away. Frieza uses this to betray him and try to finish him off... Which makes Goku blow him away.
- In ''One Piece', the Fishman Arlong kicks dogs uncountable before Luffy finally goes to take him out. Their fight escalates higher and higher, but when Arlong says that Nami will be his slave and nakama, he doesn't last five minutes before Luffy kicks him through an entire building.
- Sousuke finally killed Gauron in Full Metal Panic! when, lying, he told him that Kaname had been raped and killed.
- In Super 8, Overmeyer steals Joey Lamb's locket--the last memento of his late mother. Although this isn't really the most callous or gruesome thing he does, it carries the most emotional weight. Minutes later, Overmeyer is brutally slaughtered by the alien, and before abandoning the corpse, Joey takes the locket back.
Hello, Unknown Troper. You'll need to get known to lend a hand here.