Just because an anime villain looks badass doesn't mean they'll meet their end with dignity. When the going gets tough, seemingly horrid antagonists often devolve into fits of screaming, crying, and begging for mercy.
Humiliating anime villain defeats are especially satisfying when the evildoer is an awful person. Watching Sword Art Online's Nobuyuki Sugou wail like an infant is amazingly gratifying, as he spends most of the series sexually assaulting and coercing innocent people.
Things get a whole lot less fun when a sympathetic anime villain falls apart. It's hard to watch Light Yagami of Death Note meet his end, as fans know the boy's heart was in the right place at the start of the series.
Speed-o'-Sound Sonic wholeheartedly believes he's Saitama's rival. If this were a conventional anime, the two would have a no-holds-barred battle to decide the most powerful warrior.
However, this is One Punch Man, so pretty much all shonen tropes go out the window. Saitama easily defeats his so-called rival – who he has no particular interest in – by punching him in the crotch. Way to bring a villain back down to Earth.
Nobuyuki Sugou is one of most hated anime characters of all time, so watching him go down in a blaze of shame is deeply satisfying.
Sugou, AKA Oberon in the virtual world of ALfheim Online, traps Asuna's consciousness in a cage while her body lies comatose in the real world. He then persuades Asuna's father to accept a marriage proposal on her behalf, while in the game he repeatedly molests her.
Kirito defeats Sugou's digital persona, and also manages to foil his plans in real life. In-game, an act of deus ex machina gives Kirito total control of the world's settings. He turns the game's Pain Absorber program all the way down to zero, so when Sugou's character gets hurt, he feels it in real life.
When faced with actual pain, the haughty Sugou is reduced to a sniveling wreck, and he's easily defeated. Back in reality, Sugou tries to get revenge by attacking Kirito in a parking lot, but the hero overpowers him, then turns him over to the police. It's easily one of the most satisfying moments in Sword Art Online.
Despite the show's generally barbarous tone, some of the villains in Hellsing Ultimate go down in ridiculously embarrassing ways. Luke Valentine is a vampire who thinks he can murder Alucard without breaking a sweat. After Alucard severs his legs and mocks him for not being able to regenerate quickly enough, it's pretty obvious he made a mistake.
For a time, Light Yagami believed he was a god, but when he's revealed to be the serial killer Kira, his divine composure evaporates. He implicates his co-conspirators, tries (and fails) to talk his way out of the situation, and ends up screaming, sobbing, and begging for mercy until Ryuk finally kills him, as he'd promised to do from the start.
Watching Death Note's evil protagonist unravel is equal parts satisfying and distressing. When Aizawa and Matsuda – two adults who knew Light as a child – react to his humiliating death, it's hard not to feel choked up, as they truly believed he wasn't a murderer.