Doumon from the Tamers Forever Series is a manipulative, condescending and arrogant bitch who casually dismisses Takato as a threat, treating him like a small child who needs to learn his place. Which makes it all the more satisfying when Takato calmly points out to her just how completely and utterly screwed she is.
Queen Of All Oni: Lung sees himself as the next Daolon Wong, and is utterly convinced of his brilliance and power. And yet, when his plan to break Jade to his will fails, he simply blunders ahead with it, even when it's clear he's killing her. This gets him killed by her vengeful bodyguards.
Veran in the The Legend of Zelda fic Wisdom and Courage. While she is indeed very powerful and dangerous, her massive arrogance, tendency to Kick the Dog as much as possible, and her constant underestimating of Link and Zelda place her in this category. In fact, during her fight with Fierce Deity Link in chapter 29, the minute she realizes that Link is more than a match for her with the Fierce Deity's power even with the Triforce and Majora on her side, she bails.
Rosario Vampire: Brightest Darkness Act III: Throughout chapters 30 and 31, Kano simply laughs off the girls' threats as he's blackmailing and photographing them, confident that, between the pictures he's taken and the group's current shaky situation in the academy, he's untouchable. He's proven wrong at the end of chapter 31 when Luna eats the entire back half of his head as he's about to force himself on Mizore.