Tafsir of Al-Qalam 68:10

"Every habitual swearer" (hallaf): one who swears excessively, whether in truth or falsehood. This alone is sufficient as a deterrent for anyone accustomed to swearing, for it is made the starting point of the censure and the foundation of what follows. It indicates a lack of awareness of the greatness of Allah, the Almighty and Majestic, which is the mother of all evil in belief and deed. Some have mentioned that excessive swearing is blameworthy even when truthful, due to the audacity it shows toward His name, the Glorified and Majestic. This prohibition also serves to incite and stir [the Prophet], meaning: persist in the state you are in of not obeying every habitual swearer.

"Mean" (mahin): one who is contemptible in opinion and judgment. Al-Rummani said: The mahin is the base one, due to his abundance of ugly behavior, derived from mahanah (meanness), which is scantiness/lowliness. Ibn al-Mundhir and 'Abd ibn Humayd recorded from Qatadah that he said: "He is the one who is excessive in evil." Ibn Jarir and others recorded from Ibn Abbas that he is "the liar."