A dog is a dog, no matter the size!
Polite behavior and obedience training seems to be a largely "big dog" dominated activity. It is very easy to simply scoop up a little dog that is barking at people, not care( because he doesn't weigh much) that he's jumping on people, not be too concerned about growling and snapping because their mouths are too small, and even not mind picking up little dried-up poops in the house because they "arn't really that messy."
No matter the size, all dogs are looking for leadership and guidance. Problem behaviors are a cry for help, no matter if your dog weighs 5lbs or 105lbs. A growling Chihuahua may as well be a growling German Shepherd--they are both dogs and deserve to be treated as such. Ignoring little dog bad behavior is more than a dog having a "Napoleon Complex"--it's a red flag to the needs of the "dog" inside that little dog not being met.
I love this picture because 3 little dogs are rocking it! Chi Chi and Jackson are waiting at the open front door in down/stays for me to say "let's go!" and walk. My boy Leo (a previously to-be-euthanized-for-biting little dog, who spent more time in his old life being spoiled like a baby than being treated like a dog) working it out on the treadmill leash-free!
Little dogs are still dogs, and may surprise you how much they are looking for leadership!