Praise be to Allah.
Some people say when they are arguing, “I am going to think of you as if Allah never created you.” The meaning that first springs to mind when hearing this phrase is: I am going to regard you as nothing or as non-existent, and the like, hence I shall do to you whatever I want, and you will never be able to get rid of me or fight back, because you are as nothing.
This is what this expression seems to mean.
But what the Muslim should do is avoid such phrases, because the literal meaning is not sound or appropriate. It is not permissible for the Muslim to come to something that Allah (may He be exalted) has created and think of it as if it was never created, because it is not appropriate to think of something that exists as being non-existent.
The Muslim is enjoined to guard his tongue and avoid ambiguous phrases that could be misinterpreted, especially phrases that refer to Allah (may He be exalted) or His Prophets or His religion.
However, it is not appropriate for a dispute between Muslims to reach such a point that a Muslim threatens to kill his brother, because killing a believer is one of the gravest of major sins. Similarly, threatening and scaring a Muslim – when there is no reason that would make doing so permissible – is also a major sin.
This phrase also constitutes tyranny and transgression, and boasting of one’s strength, which is not a praiseworthy action, as is indicated by the verse in which Allah (may He be exalted) says (interpretation over the meaning):
“And do not turn your cheek [in contempt] toward people and do not walk through the earth exultantly. Indeed, Allah does not like everyone self-deluded and boastful”
The Muslims are enjoined to take one another as brothers and be gentle towards one another, to speak good words and to treat one another with compassion. Allah (may He be exalted) says (interpretation of the meaning):
“Muhammad is the Messenger of Allah; and those with him are forceful against the disbelievers, merciful among themselves”
And they should avoid getting into disputes by using gentle words, as Allah (may He be exalted) says (interpretation of the meaning):
“Repel [evil] by that [deed] which is better; and thereupon the one whom between you and him is enmity [will become] as though he was a devoted friend”
And Allah knows best.