Is laughing at a teacher's humiliation considered envy, or is laughing when a sin or act of disbelief occurs, or laughing when someone mocks religion to avoid their animosity, an act of disbelief?

A Muslim does not exit Islam except with certainty. Waswasah (whispering of Satan), error, compulsion, and mere self-talk do not lead to disbelief, as Allah Almighty says: (And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended), and as the Prophet, peace and blessings be upon him, said: (Indeed, Allah has forgiven my Ummah for whatever they whisper to themselves, as long as they do not act upon it or speak of it), and (Indeed, Allah has forgiven my Ummah for error, forgetfulness, and what they are compelled to do).

Your laughter at the teacher's statement, "Congratulations, this will destroy the phone," is not mockery of religion, as it has no connection to religious rulings. So, do not pay attention to whispers.

However, laughing upon seeing a sin or mockery of religion is not permissible. Rather, one must rebuke the doer, and if they do not respond, one must leave the place, as Allah Almighty says: (Then do not sit with them until they engage in another conversation. Indeed, you would then be like them). Smiling or laughing in this situation makes one a partner in sin if it is out of approval, or a great sin if it is not out of approval, indicating weakness in glorifying Allah and His rituals. It is obligatory to glorify the rituals of Allah and to prioritize Allah's pleasure over people's pleasure. Whoever seeks Allah's pleasure through people's displeasure, Allah will be pleased with him and make people pleased with him. And whoever seeks people's pleasure through Allah's displeasure, Allah will be displeased with him and make people displeased with him.