When are the following statements considered backbiting (ghibah): disliking someone, describing a company as fraudulent, jokingly calling an aunt "O teacher," criticizing Muslim rulers, or narrating an incident of humiliation by an unknown person?

Simply saying "I hate so-and-so" is not backbiting if it does not involve disparagement. Love and hatred are matters that may not be controllable, but injustice is not permissible. Saying "this company is thieves" is not backbiting because it is an accusation against a general entity, and backbiting only applies to known individuals. Saying "O teacher" is not problematic unless it is done mockingly or derisively, and it is not backbiting. Commenting on the publicly known actions of some rulers is not backbiting because mentioning a transgressor for what he has publicized is not backbiting. Talking about an unknown person for what he did is not backbiting as long as he remains unknown.