Is it permissible for me to say, "The curse of Allah be upon me if I am among the liars," and is this an oath sworn by other than Allah?

It is authentically reported that the Prophet, peace be upon him, said: "A believer is not a slanderer, nor a curser, nor an obscene person, nor an abusive one." And the statement "May the curse of Allah be upon him if he is among the liars" is neither an oath nor a sworn affirmation, and whoever breaks it incurs no expiation. The expiation for this type of utterance is only seeking forgiveness.