People should speak Good Words with Politeness

Allah commands His servant Muhammad ﷺ to tell the believing servants of Allah that they should address one another in their conversations and discussions with the best and politest of words, for if they do not do that, Shaytan will sow discord among them, and words will lead to actions, so that evil and conflicts and fights will arise among them. For Shaytan is the enemy of Adam and his descendants, and has been since he refused to prostrate to Adam. His enmity is obvious and manifest. For this reason it is forbidden for a man to point at his Muslim brother with an iron instrument, for Shaytan may cause him to strike him with it. (Imam Ahmad recorded that Abu Hurayrah said: "The Messenger of Allah ﷺ said:

«لَا يُشِيرَنَّ أَحَدُكُمْ إِلَى أَخِيهِ بِالسِّلَاحِ، فَإِنَّهُ لَا يَدْرِي أَحَدُكُمْ لَعَلَّ الشَّيْطَانَ أَنْ يَنْزِعَ فِي يَدِهِ فَيَقَعَ فِي حُفْرَةٍ مِنَ النَّار»

Commentary

Using foul or harsh language is not correct, even against infidels