A Chihuahua knows one thing to be true: His pack (which is all members of the household including all humans and all pets) needs to have a leader. The leader is often referred to as the Alpha. Whether a dog lives with just one owner or is part of a huge family of humans can all sorts of other pets, there simply must be an Alpha. The Alpha must be listened to. It is the canine way.
With dogs, the true Alpha is always obeyed. When he gives a command, it is followed. When he calls, his Betas come. He sets the rules and at the same time, he is respected and loved. When a dog has this sort of environment, with clear hierarchy, his world makes sense to him. Everything is as it should be and dogs with this understanding are well behaved, happy and listen to their owners with enthusiasm. They know that they will be cared for, protected and have a peaceful feeling of safety.
To refuse to listen to his leader is akin to initiating an unbalanced pack and dogs will not do this. Only if an extended amount of time has gone by in which an owner shows weakness as leader, a dog may then step in to take his place…and this is the main reason why a dog that previously listened no longer does so.
If a Chihuahua does not listen, this is due to 1 of 3 things:
He does not know who the leader is, so with no other choice, he has taken on that role himself. No one has challenged him to take the lead, so he remains doing what he wants, when he wants and that includes not listening.
He is unsure about the hierarchy in the house, so he is held to canine instinct to engage in a power struggle. He will test his human(s) to see if his owner will step up or if he himself will need to take on the role of leader.
He truly believes that he is the leader due to the owner(s) mistakenly reinforcing this idea. At one point he was not sure, however days/weeks or months of evidence has 'proven' to him that he has been declared the true Alpha.
When a Chihuahua is in any of these positions, he/she will not listen to his owners. There may be random times that he appears to come on command or perform a task when asked…and he may even cuddle or appear to be super attentive… however this is just a matter of the dog doing these things when he wants to.