asuming higher income having a negative correlation with profanity.
I wouldn't be so sure. Other decadent behaviors, like drinking alcohol, are positively correlated with income.
I've heard it be explained as wealthier people drink more on average but poorer people are more likely to suffer from severe alcoholism.
Regarding cursing and income, I couldn't find much on this but this one study on tweets did pop up:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138717"On the other hand, an opposite linear relationship is present for ‘Swearing’ (Topic 99). Swear words are used more by people with lower incomes which suggest that they use more informal language. The same behaviour holds in general with topics that contain more personal language or words with alternative spellings (topics not shown here). This suggests that in general users of lower income use social media more for personal communication, while the ones with higher incomes use it for more ‘professional’ issues;"