Curses and cursing have trends. And the society goes for highest taboo which exists. Example from history:
- Religious taboo (medieval) – people used to believe that saying deity name would actually hurt such deity. OK, your setting can skip this
- Bodily functions: Naming people as taboo bodily parts. In our case these are organs used for sexual reproduction and/or bodily functions, namely defecation. While you rule this part out, still there can be body part which is considered taboo and “talk to the hand!” may be purely offensive
- Racial and race based: You either can use slang word for one race as offensive or abusive. Also to this group you can have social status in the group, so “you are beggar” can be also offensive
- Mentality and psychological based (current trend in our society). Any word connected with fact that such person may have low IQ is considered really abusive in our society.
Start with having some taboo If you are intelligent species, you do not talk about something. We like to have something hidden, because it does not go well with our “perfect” world.
Good picks to start:
- A person who is perceived as negative. Earth example: Adolf Hitler