Is it permissible to swear and curse when upset?

So firstly, it's a good sign that you regret it. We know the Prophet said in Sahih Muslim that using vulgar language is not befitting of a Muslim. In fact, in the hadith in Sahih Bukhari, the Prophet said, 'Your duty is to be gentle in terms of your words when you speak to others.' And remind yourself of the hadith where the Prophet said that he grabbed his tongue and he said, 'Beware and stop this because people will be thrown into Jahannam because of what their tongues had said.' And thirdly, remind yourself that the angels are writing down every single thing that we say and that will be in our good deeds or bad deeds. So whenever you feel like that, just stop yourself, just remind yourself of one or any of those hadith and inshaAllah that will be able to help.