This is where a dog is really, really mean to anyone and everyone, anything and everything, whether rabid, genetically tampered with, or trained from birth to be that way. If the dog has an owner, then sometimes even the owner can get on the dog's wrong side from time to time.
This type of dog is not a Hellhound, but is a rather normal and standard dog aside from his viciousness. He CAN be kicked, but 9 times out of 10 Failure Is the Only Option where that is concerned. Indeed, kicking him successfully will often make you look reasonable.
NOT a savage wolf, though given his temperament, he may as well be.
May be an Angry Guard Dog or a Bully Bulldog, although those types usually guard homes or properties. The Vicious Dog, on the other hand, is mean regardless of his size or breed and regardless of whether he's a pet/guard dog or not.
The trope takes its name from the frequent signs on the front of homeowners' gates, usually reading simply "Beware Of Dog," that warn visitors about the potential badness of the resident pooch. Incidentally, if you put up one of these signs, be warned - this will not reduce your risk of getting sued if the dog attacks someone. In fact, it weakens your legal defense, since the sign proves you know the dog is dangerous.
- Parodied in The Far Side, where a shifty individual peers from behind a tree at an approaching salesman in a yard bearing the sign "Beware of Doug."
- The poodle in There's Something About Mary. Played for Laughs.
- "The Beast," the giant Mastiff dog in The Sandlot, who terrorizes the land next door to the titular sandlot where the kids play baseball, to the point that he's become something of a legend and the kids have to take great care not to knock their baseballs over the fence to where he is; getting back a Babe Ruth-signed ball drives the second half of the movie. Subverted—he turns out to be a Gentle Giant once the kids get to know him.
- The sled-dog Demon in Snow Dogs behaves this way due to a sore tooth.
- The blind girl's dog in The Beyond usually wouldn't be so vicious, but since they're in a possessed hotel, it influences the dog to attack his owner.
- Max, the Tibetan Mastiff in the 1993 film Man's Best Friend, is this due to being genetically enhanced.
- The 1977 film The Pack is about a group of dogs that behaves this way.
- The 2006 horror movie The Breed has the protagonists being stalked by a group of dogs that embody this trope.
- Chopper, Milo Pressman's dog in Stand by Me, has this reputation. Subverted.
- The 2015 horror film Night Of The Wild is about dogs in a peaceful town being affected by a strange green meteor that makes them Brainwashed and Crazy. Led by a wolf-like dog, they all start turning on their human owners, and it's hinted in the Downer Ending that the meteor has affected other towns and dogs too.
- Stephen King's Cujo, by virtue of rabies. Before getting infected, he was a Big, Friendly Dog.
- In Diana Wynne Jones's Castle in the Air, Jamal's dog is like this.
Jamal: I believe in free will. If my dog wishes to hate everyone in the world but myself, it is free to do so.
- Farmer Maggot's dogs Wolf, Fang and Grip in The Lord of the Rings.
- Wolvogs, the genetically engineered dogs of Oryx and Crake, will rip you to shreds without hesitation.
- Survivor Dogs:
- The first arc has the Fierce Dogs, a pack of Doberman pinschers always eager to fight someone or kill something (though there are some exceptions like Storm and Arrow).
- The first arc also has Terror, a huge mastiff/pit bull mix who rants about being a servant to the Fear Dog and treats his packmates badly.
- Our Miss Brooks: Mr. Whipple's guard dogs in the episode "Mr. Whipple".
- WKRP in Cincinnati: As a Running Gag Les had a bandage somewhere on his person in every episode. (This stemmed from actor Richard Saunders having a cut on pilot taping day.) Eventually we learn that he has a vicious dog at home.
- Remington Steele plays with this in a season one episode when Laura and Murphy break into a suspect's house. Murphy, having seen the "Beware Dog" sign, is paranoid until he sees the old, lazy Bassett hound lying on an armchair.
- The "overly aggressive to the owner's detriment" sort of dog is a constant feature Victoria Stillwell's dog-training program It's Me or the Dog.
- Averted on the Animal Planet series Too Cute; whenever breeds that are popularly considered "dangerous" are featured, the narrator is quick to emphasize that with proper training, they make wonderful pets.
- Voyagers!, "Voyagers of the Titanic": A time jump lands Bogg, Olivia, and Jeff in Louis Pasteur's office, where the rabid dog he keeps to help his rabies experiments has gotten loose. Olivia backs it into a corner, against Bogg's advice, and it gets past her and bites Jeff's hand.
- Popular parody: Picture of a firearm. "Forget the dog, beware of the owner."
- Shadow's dog Interceptor in Final Fantasy VI, only being obedient to Shadow himself and nice to Relm on their first meeting.
Shadow: Leave us. The dog eats strangers...
- The Runaway Dogs from EarthBound will attack anyone who stands on their way, even defenseless children. On the other hand, once you've gotten enough levels, you can boot them all you want as revenge and put them down in one shot at that.
- In Mass Effect 3, Wrex comments that if Tuchanka has a temper, its name is Kalros, The Mother of All Thresher-Maws.
- A vicious dog guarding a farmyard threatens the two boys in Brothers: A Tale of Two Sons. They get past him by alternately distracting and then rushing through the yard.
- The Feral Hounds introduced by poachers into the ecosystem of an alien game planet in Carnivores Triassic fit this role, both for viciously attacking the player hunter and for slowly killing off some of the native fauna.
- The Big Top level in CarnEvil has undead feral poodles wearing clown collars.
- Angry dogs are among the obstacles you must run away from in Inside. If you see or hear one, run the hell away, because they are fast, persistent, and want you dead. And since the player character is a defenseless little boy, you have no choice but to run away and avoid them.
- Fallout 4 has feral mongrels that behave a bit like a wolf pack, coming at you many at a time. Same goes for the raiders' dogs and the super mutants' mutant hounds, which send bone-chilling howls down your spine once they notice you.
- Undertale plays vigorously with this trope, mostly subverting it. While several guard dogs do in fact attack you on sight, and humorously worded signs forewarn about a few of these encounters, not all of these dogs are particularly ill-tempered, the ones who are only really act this way around unfamiliar humans, and in every case you can literally Pet the Dog and befriend it. The sign next to the Lesser Dog's house parodies the classic warning: "aware of dog, pls pet dog."
- Oscar the dog from Kick Buttowski.
- Gru's... dog?.. thing from Despicable Me, who strikes fear in everyone, even its master. That is until Agnes comes along.
- While looking for a suitable canine dance partner, Bill Dauterive of King of the Hill is talked into adopting a muzzled Rottweiler by the two snickering attendants at the pound. Then he takes it home and undoes the muzzle... suffice to say, Hilarity Ensues.
- The first episode of Boo Boom! The Long Way Home a pack of really mean street dogs attack the protagonists, forcing Boldsteed, Christopher, and Aurelia to fight them off.
- Earl from Rocko's Modern Life. The only one who's not afraid of Earl is Bev. Though Earl's temperment is somewhat justified, as he was used for horrific experiments and Escaped from the Lab.
- In Oliver & Company, Sikes has two nasty dobermans, which he uses to intimidate Fagin and his dogs.
- Truth in Television where dogs who are trained and bred to fight are concerned. Rottweilers in particular have gotten a bad reputation for being vicious because of this.
- In other cases, it's just a case of irresponsible owners who never claim responsibility for their dog's indiscriminate hostility.