Our Sages taught that one must be careful to not anger even a gentile child. The Talmud Yerushalmi tells the story of a gentile swine keeper who was attacked by Jews. Eventually the man became a king and if not for Rabbi Yehoshuah who had treated him well, he would have decreed devastation upon the Jews.
It is not right to quarrel with any gentile, for one does not know where it will lead to. Even if the only result will be that the gentile will curse the person, that should not be taken lightly, for the Sages taught, “Let not the curse of even the simplest person be light in your eyes.” On the contrary, one should be the first to offer greetings to every person, Jew or gentile alike.