Is my laughing at a teacher’s mockery of my classmate considered backbiting (Gheebah)? What are the consequences for me? Am I sinful if I do not defend the honor of a Muslim who is being backbitten by a teacher in a gathering? And am I accountable for anything if I compare one female teacher to another male teacher?

Merely laughing at what happened in front of a person, without having caused it, is not considered backbiting (gheebah) or mockery. The forbidden backbiting is mentioning your brother with what he dislikes. If you are unable to denounce the backbiter, or defend the honor of a Muslim, and you fear harm, then denounce it with your heart, for that is the weakest of faith. Your informing your brother about your personal impressions of people, and explaining the reason for your desire to move from one teacher to another, is not backbiting, especially if your intention is to advise, and with your praise of her.