What should I do if I get cursed at and the words are very unpleasant?

I think "unpleasant" is because you have a sense of shame and dignity—simply put, a sense of face. People who open their mouths and speak indecent words don't need this thing. Their parents, family, and teachers failed to instill the basic sense of shame and etiquette necessary for living in human society. This thing often called "cultivation" is a high-end luxury item that they have never experienced in their lifetime.
In low-level behaviors like "cursing people," because their bottom line is lower than yours, they can dance in the low realm you cannot reach. But you are helpless because of self-imposed limitations. In ancient times, some beggars attacked others by throwing offerings, but you can't retaliate in the same way because holding that thing in your hand is already an attack on you.
Since graduating from high school, I haven't engaged in pointless verbal disputes, but I participated in debate competitions for five years in college, from freshman contests to the Xinhua Debate Golden League, experiencing the verbal battles of many language elites from North China: carefully scrutinizing language loopholes along logical lines, citing classics and drawing from various sources along knowledge routes, and subtly questioning opponents amid laughter and joy along humorous routes. But none of them relied on lowering their bottom line to fight with foul language like a shrew rolling in the street, because this way of verbal sparring exceeds their cognitive limits.
Trying to make such people understand genuine human communication is like giving dung beetles a high-end banquet—completely futile. There's no need to worry about this; after all, silkworms and maggots certainly can't compare in eating offerings, but you produce silk and luxury goods, not decomposers in the biological circle. There's no need to forcibly cross into their realm. People who rely on their verbal bottom line to stand in the world, apart from themselves and their parents, cannot harm anyone and pose no real threat.