As a dog owner for more decades than I wish to admit, I feel I need to correct a few misconceptions.
Small dog owners know their dogs are the devil's spawn in public, but they have a hard time reconciling that with the fact that their little dog is pure love towards them at home. Because they are small, they get to cuddle with their owner like bigger dogs cannot.
Little dogs can indeed be yappy, aggressive, socially unsavory AND cute. These things are not mutually exclusive. Just ask anyone ever bitten because they tried to pet that adorable Pomeranian or Yorkie. They lure you in with cuteness so they can strike without warning.
..."you have an untrained dog..."
I find it adorable that you think a micro hellspawn is trainable.
EDIT: I thought it was clear that this was meant mostly tongue and cheek.
Micro hellspawns are created by behaviours such as picking up dogs during social interactions or to calm them. Also raising voice to tell the dog off for barking or being aggressive. But then also lack of socialisation and mental stimulation, especially since many small dog breeds are actually working dogs.
Basically exactly what to do if you want to train an aggressive, loud dog very rapidly. There's no such things as an untrainable dog. If a dog is behaving that way, it's doing exactly what it was trained to do by the owner's poor handling and knowledge.