Why do you thank people? Do you ever thank those who are rude/impolite/insulting? For what and why?

I guess maybe saying Thank you is just part of me as I usually say it to anyone. Helpful or not. Sometimes it can be sarcastic to rude people and insulting people? I don't give the time of day too. But 99% of the time, I will always say Thank you as I don't want to be like them.

Hi, Rosie! The last person I said thank you to that was rude was a guy who told me I was as fake and plastic as his credit card. I said a thank you that was dripping with sarcasm. The rest of the time I just say thank you to be polite.

Someone else's rudeness is not an excuse for me to forget my manners.