Moral Relativism
Moral relativism takes one step further than moral subjectivism. Not only are there no moral truths, only moral opinions, but everyone's opinions are right for them.
Bob feeds the orphans. This is a good act because Bob simply feels that helping vulnerable children is a good thing to do and makes him feel good. Sam does not feed the orphans. This is a good act because Sam does not feel that his involvement is needed at this time.
Consequence of Subjective Morality
If you truly believe that morality is subjective, then you must accept the reality of moral relativism as well. If Bob says that bloodletting is a good moral action, then by subjective morality it is a good a moral action for him. If Sam says that bloodletting is not moral, then by subjective morality is it bad for him. Sam and Bob have conflicting opinions but the moral relativist says they are both correct.
You have to hold in your head that bloodletting is both good and bad. Each different person defines a different set of morals, and according to subjective morality, those are true morals for each of them at the same time. But how can bloodletting be both moral and immoral at the same time, for different people?
Moral relativist have to believe that the morality of Bob is independent of the morality of Sam. If you go to Bob's house, then bloodletting really is good for you. But at Sam's house it really is bad.