Flag the comment/message for mod attention. If the offense is found to be serious mods may consider keeping the user in cool down period somewhere between 1 week to 1 year. But if the offense is very much serious, they may suspend their account indefinitely.
By offense here I mean violation of code of conduct.
But suspension doesn't guarantee if they won't return. After all, creating an account on SE is free :)
Sometimes "you" might also like to see the other side of the coin too. May be that user is not targeting specifically "you". They might be disagreeing with your thoughts. And IMHO, disagreements should encourage looking for actual facts or open windows for alternate ways of thinking.