It depends. Sometimes people are rude, because you won a hand, and they just
have to tell you how dared you dumb fish to crack their Asses ^^ with 45.
But it is also very often, that people try to set off you on purpose. They know, that some things go under the skin and they use them.
If we consider, that the purpose of poker is making money, not only by knowing your pott ods, but also by knowing a little bit of human psychology, I would say it is a totally legitimate move, to try to make someone go on tilt
through the chat. But it can also backfire in so many ways. For example if you are really a pro and are making money from some recreational fish, then you want recreational players to play with you again and again. So the edge you can get through chatting nasty is immediately lost, if the fish won't play with you again. Or a fish can suddenly stop being a fish.
People can tighten up, they can ajust and they can be revengefull.