Bad behavior such as lying, cheating, backbiting, slandering, etc., are haraam even out of Ramadaan and should be avoided all the more in this sacred month.
Abu Hurairah narrated that the Messenger of Allah (ﷺ) said: “If anyone does not abandon falsehood and action in accordance with it, Allah has no need that he should abandon his food and drink.”
Abu Hurairah narrated that the Messenger of Allah (ﷺ) said: “Whoever does not give up forged speech and evil actions, Allah is not in need of his leaving his food and drink (i.e. Allah will not accept his fasting).”
Abu Hurairah narrated that the Prophet Muhammad (ﷺ) said: “Fast is a shield; when one of you is fasting, he should neither behave in an obscene manner nor foolishly. If a man fights or abuses him, he should say: I am fasting, I am fasting.”
(Sunan Abu Dawud (English Trans.), vol.2, p.648, no. 2355-6)
(Sahih Buhkari, Book of Fasting, Chapter 8)