I interact with a lot of breeds for my day job. The only two consistent factors I've come across are:
- Chihuahuas are the most high strung, angriest dogs you'll ever meet. To quote Scrubs: "They're bastard-coated bastards with bastard filling". They're angry at the world and will let everyone know it.
- Pugs should not exist. Whatever crossbreeding humanity has done to turn them into what they are today should be reversed. Even fully healthy ones are barely able to breathe, and if they get sick or injured (which is very common for them), they basically become lumps of flesh that wheeze. If you want a similar looking dog that can actually function as a dog, get a Frenchie.