Is saying "Don't lie, you Musaylimah the Liar" to a person who lies considered an act of disbelief, knowing that the intention is to taunt him with lying, not to accuse him of disbelief?

Calling someone "Musaylimah the Liar" is not an act of takfir (declaring someone an apostate); rather, it is a repulsion from this description. This statement may be prohibited if it causes harm to a Muslim, based on the Almighty's saying: {And those who harm believing men and believing women for [something] other than what they have earned have certainly borne a slander and a manifest sin.} (Al-Ahzab: 58). Harming believers can be through evil words and deeds, and it may include taunting them with something burdensome to them. Slander, in general, is a sin that warrants ta'zir (discretionary punishment) if the statement is not an accusation of illicit sexual conduct, whether it is by calling him "O disbeliever," or "O hypocrite," or other descriptions that do not apply to the slandered person, or that bring him shame and harm.