Is laughing at a teacher for unintentionally repeating a word considered "hamz and lamz" (slander and backbiting)?

Deliberately gesturing at a Muslim's defect with the eye, hand, head, or otherwise, falls under backbiting (hamz and lamz) and forbidden gossip (gheebah), because it is an attack through speech and gesture, and mentioning a Muslim with what they dislike in their absence. Al-Nawawi said in Al-Adhkar: "Gheebah is your mentioning of a person with what is in them that they dislike, whether you mention it with your words, or your writing, or you symbolize, or point to them with your eye, or your hand, or your head, or similar."

However, if laughter overwhelms a person without intent, they are not held accountable for it, because it is due to the predominance of human nature. 'Iyad said in Ikmal al-Mu'allim: "Laughter in such a case is not commendable, nor permissible, unless it stems from an overwhelming human nature. As for intentionally doing so, it involves gloating over a Muslim and mocking their misfortune."

Al-Nawawi said in his commentary on Sahih Muslim: "This contains a prohibition against laughing at such things, unless it is an overwhelming force that cannot be repelled. As for doing so intentionally, it is blameworthy; because it involves gloating over a Muslim and breaking their heart."