I don't know where you saw Tamil guys use bad words. If used. Then it would be due to an issue with the opposite person.
Apart from that they never use words. I have been with many hindi speaking friends. Educated ones.
They use behen chod, Madarchod as a slag very often during conversations. They use those as a word fuck in English.
You will never see Tamil guys use those words in Tamil while having conversations. They use the word machi (cousin)
