I have two Chihuahuas! Bella is a three year old chihuahua she is aggressive she doesn't like strangers or other animals. She hates when someone comes to me or to the house even if they walk in the street. But just because some chihuahuas are mean doesn't mean they are ALL mean!! Sadie is a 1 year old Chihuahua and she is so very sweet she doesn't know a stranger she is a lap dog she is about 2 pounds. Chihuahuas are very smart they learn fast. Sadie loves people and all animals, she is a little scared of big dogs but thats because she is so small. It depends on where you get the chihuahua how is was raised when with the breeder and you have to take it out and meet other people and dogs all the time. YOu have to train it well or it'll have a chance of being aggressive when older. I also have a doberman and the chihuahuas love her. (sadie and bella we not bought from the same people.)
Hope i helped!
Good luck!