At the end of a Penny and Aggie storyline, Charisma rants to her illegitimate son's face that he exists to ruin her life, after a series of events he had no control over, in front of her boyfriend. Needless to say, he leaves her soon after.
In Sluggy Freelance Aylee's evil clone gets one of these after she goes through her corporate executive transformation. She attacks the gang's Halloween party and leaves all the guests unconscious outside and taunts Riff with the knowledge that she can kill him and everyone he knows so easily.
Vaarsuvius threatening Elan with death when Elan says that he will not cover up for Vaarsuvius killing Kubota. In addition to suggesting that Elan had an affair with Therkla behind Haley's back. Note that Elan is hir team-mate.
Belkar constantly complains about not getting to kick any dogs. Although, he does eventually cross the line with his teammates when he kills the oracle.
Yukyuk here. He had no way of knowing that Mr. Scruffy was an enemy - he just decided to shoot a cat for fun.
He could have chosen a much less mean way to put it, but he does have a fair point: he and Fay are fuck buddies with few-or-no strings attached, so expecting exclusivity is pretty strange. And if she wants something more serious, she could always ASK, rather than trying to browbeat him into it.
Misty Snow from Shadowgirls. She was racist at the age of 5, and when she grew up, she became a teenage Queen of Jerkass. Her biggest feat in kicking a dog? She made Lin betray her best friend Becka for popularity, and led her in a trap, but instead of embarrassing her in public, like Lin thought it would end, Becka almost gets raped by three guys. And Misty was meanwhile playing with Lin's guilt, and thinking about it made Fate Worse Than Death even worse.
And if you think Misty's bad, just wait until she becomes Possessed ByMotherHydra, who surpasses her in kicking a dog like hell. And she has this promo art.
Nemen Yi, the Chosen of Battles in Keychain of Creation. When she first shows up, her moral status is indeterminate: sure, she's trying to sequester the group's precious artifact, but it had just been stolen by the villains for world-ending purposes. Then, after one of the team gets it back, the Chosen of Battles looks like she's ready to throw down on the group — until Marena points out that that would be illegal. Fortunately, the conundrum of whether we're supposed to sympathize with Nemen Yi or not is solved in the very very next strip, as she immediately chooses to try and steal the artifact and bait the rest of the group into attacking her first (so she can "defend" herself) by attempting to behead Secret, on the legal technicality that even though she is a defector from team evil and working for the protagonists, she's still an Abyssal Exalted. Going straight for The Woobie's neck just to get around a bureaucratic roadblock in your path is what we call "a signal".
Cyanideand Happiness uses this, taken as literally as possible, as the entire punchline, and stinger, for their latest short.
But I'm a Cat Person takes this from the dog's point of view. The kicker's identity is still a mystery, but the aftermath inspires the heroes (at least, one of them) to commit to being on the dog's side.
Seymour, the Knight Templar vampire hunter from Nosfera does this when he kills some monsters after they had ALREADY SURRENDERED.
Although, the one time she fought an actual dog (the Big Bad Jack Noir) she was being heroic.
In Captain SNES: The Game Masta, Mother Brain (a Harmless Villain in the show the comic is based on) takes it half-literally by smacking Captain N's dog Duke into a pit filled with Omega Energy just to spite the Captain. This upsets not only her enemies, but also her henchman, King Hippo.
In Our Little Adventure, Peganone, Eva and Randi were attacked by Angelo. Not only they lost the fight, but Angelo ended up magically forcing the Paladin Eva to slay her own horse. The dramatic effect of this was lessened by her horse easily being able to outrun her, and Angelo getting bored and calling it off. It was still very cruel and unnecessary.
The Comic Irregulars: If you're going to have your bad guy do something despicably evil by destroying something huge, make it something that the PCs care about. Something they've fought for and made sacrifices to save.