If you refer to not culture-specific moralities (for those are objective in a sense), but a personal morality, then I believe you've already shown one way of distinguishing subjective morality from objective morality. If subjective then morality is unstable, changing with the mood and desire of the person, and consequently always unclear, never certain; and because in effect he is subject to himself, rather than to an higher authority, this morality therefore is not a morality at all, only a self-conceited capriciousness.