Avatar: The Last Airbender's Pakku gets a pretty excellent one before fighting Katara: "If you want to learn waterbending so badly, STUDY CLOSELY!!"
"I'm sorry it has to end this way, brother." "No you're not."
"You're clearly outnumbered!" "That's true, but you are clearly outmatched!"
"Did I ever tell you how I got the nickname Dragon of the West?"
"Taking back my city!!"
"Trust me, Zuko, it's not gonna be much of a match."
"No. It's not over."
The Legend of Korra has Korra, in the first episode confront a gang of three thugs. Surprised by the fact that anyone has the nerves or stupidity to challenge them, the confrontation leads to this exchange:
In the Season 2 Origins Episode "Beginnings", Wan says this just after Vaatu mocks him and declares that no human can beat him:
Haven't you heard the legends? I'm not a regular human anymore! (unleashes Firebending)
Tenzin gets a great one before his fight with Zaheer in Season 3:
Zaheer: Unfortunately, you don't have a choice.
Tenzin: Yes, I do. (blasts Zaheer, Ming-Hua and Ghazan across the courtyard with one move)
In Total Drama Island, by the end of the fight between Izzy and Chef in "Hide and Be Sneaky":
Izzy: Bye bye! (kicks Chef)
Ben from Ben 10 loves to spout these before turning alien and leaping into action. They tend to be incredibly cheesy, but give him a break, he's a kid.
Played with in the The Simpsons several times. In the episode "Simple Simpson" when Homer becomes Pie Man. After a series of heroic exploits and delivering multiple pastry-based one-liners just before subduing his various victims, he eventually just uses, "I have run out of pie-related puns!"
In the episode "Itchy & Scratchy Land", while fighting out-of-control animatronic Itchy and Scratchy robots with cameras, Bart says in Schwarzenegger-esque voice "Hey mouse... say cheese." followed quickly by "With a dry, cool wit like that, I could be an action hero." It's played with even further when moments later, Homer emerges from a pile of defeated robots, saying "Die, bad robots, die!... With a dry, cool wit like that, I could be an action hero."
In a Halloween episode, Homer has to think of a witty remark to say before he assassinates Kent Brockman... but when he thinks of it, he realizes that there's nobody around and so he doesn't have to say it.
In "The Return of Harmony", Twilight Sparkle gives one just before she and the mane cast defeat Discord with the Elements Of Harmony. Probably one of the most Badass ways of invoking The Power of Friendship ever.
In "It's About Time," when Twilight prepares to kick the ass of Cerberus. Yes, thatCerberus. The moment is ruined by Fluttershy, but it's still pretty awesome.
Twilight Sparkle: "Hey, Cerberus! You look like you could use some obedience training. Magic obedience training."
In "Dragon Quest," the gang of adolescent dragons make the mistake of provoking Rarity's Mama Bear tendencies. Ultimately subverted - the ponies end up retreating - but still, wow.
Rarity: Fighting's not really my thing, I'm more into fashion, but I'll rip you to pieces if you touch one scale on his cute little head!"
When PrincessCelestia breaks out one of these in "A Canterlot Wedding," the audience knows she's finally gonna get the chance to stretch her legs. And does she ever. It's quite a shame that it leads to a Did You Just Punch Out Cthulhu? moment, but it's remarkably telling that even the villain was completely stunned by her own victory.
Celestia: You may have made it impossible for Shining Armor to perform his spell, but now that you have so foolishly revealed your true self - I can protect my subjects... from you!
Both heroes and villains often break them out, with Shego especially fond of them. With everyone recovering from a cold, Shego declares, "Looks like someone's been drinking a lot of fluids — and retaining every ounce..."
King of the Hill: "That's my purse!! I don't know you!" (kicks person in the balls). Seriously, you can't tell me you wouldn't get caught off guard by some fat kid yelling "That's my purse!" then yelling "I don't know you!" before kicking your nuts into your throat is a great way to finish it.
Also, from the episode where Bobby and Joseph become professional panhandlers.
Bum: What're you gonna do, tell my mommy? Hank: No, I'm going to kick your ass up one side of the street and down the other.
Dexter's Laboratory: A mix-up involving cereal-prize decoder rings leaves Deedee being threatened by the Pony Puffs, and Dexter having to team up with Action Hank to save her. As Hank bursts through the wall with his team to save Dee-Dee from being dunked in scalding-hot oatmeal, he delivers that classic line:
Hank: Breakfast is no longer being served! Prepare to get brunched — in the face!
Numbuh 4: "Then what are you waiting for, princess? Let's dance!".
It even gets subverted in an episode where Numbuh 5 is about to rid the tree house of lice by setting off some cheese-based explosives. Right before she does so, Numbuh 2 comes running in claiming, "You have to say something cool first!"
Numbuh 2: Something like, "Say cheese, punk", or maybe, "Cheese'd to meet you"! Oh! Wait wait wait!, "Cheese—"*Numbuh 5 sets off the explosives*
Any time Bugs Bunny is forced to utter the phrase "Of course you realize this means war!" is essentially this trope at work. What comes may not be an asskicking by normal standards...but he makes sure you feel for what you've done.
From American Dad!, when the Chocodile bumps against Stan while walking away:
Stan: Hey Chocodile! Watch where you're going!
Chocodile: (Turns about and smirks) Oh HELL no. (Lunges at him)
Texas keeps trying these in Motorcity, in an attempt to emulate action heroes from the movies he's been watching. Most of them are hilariously lame.
In A Charlie Brown Christmas, Lucy uses one to intimidate Linus into memorizing all his lines. Bonus points for the number of open digits in Lucy's hand shrinking in sync with the one-liner in question.
Lucy: I'll give you five good reasons: ONE, TWO, THREE, FOUR, FIVE. Linus: Those are good reasons.