There are a variety of reasons why the Chihuahua breed can be considered mean. The first reason is their small size.
Because the animal is so tiny in comparison to other breeds and humans, they feel threatened by the large size of what they perceive as a threat. This forces them to defend themselves by growling, biting, and barking at their predator. .
Another major reason why Chihuahuas are mean is that they are naturally protective of their territory and owner.
This makes them great guard dogs, despite their small size. When an individual or another animal intrudes into what they deem as their space, the Chihuahua is provoked into its protective mode.