Is mocking others haram?

Haram Speech & character Quran · 1

Short answer

Yes. Allah says that people should not ridicule others, since they may be better than them, and should not call each other by offensive nicknames (49:11).

Evidence

Quran

يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ لَا يَسْخَرْ قَوْمٌۭ مِّن قَوْمٍ عَسَىٰٓ أَن يَكُونُوا۟ خَيْرًۭا مِّنْهُمْ وَلَا نِسَآءٌۭ مِّن نِّسَآءٍ عَسَىٰٓ أَن يَكُنَّ خَيْرًۭا مِّنْهُنَّ ۖ وَلَا تَلْمِزُوٓا۟ أَنفُسَكُمْ وَلَا تَنَابَزُوا۟ بِٱلْأَلْقَٰبِ ۖ بِئْسَ ٱلِٱسْمُ ٱلْفُسُوقُ بَعْدَ ٱلْإِيمَٰنِ ۚ وَمَن لَّمْ يَتُبْ فَأُو۟لَٰٓئِكَ هُمُ ٱلظَّٰلِمُونَ ﴿١١﴾

O ye who believe! Let not a folk deride a folk who may be better than they (are), not let women (deride) women who may be better than they are; neither defame one another, nor insult one another by nicknames. Bad is the name of lewdness after faith. And whoso turneth not in repentance, such are evil-doers.

This is general information, not a fatwa. For your own situation, ask a qualified scholar.