for all (one) cares
One does not care (if something were to happen). The phrase always precedes or follows some hypothetical situation. You can starve to death for all I care. I am not giving you any more of my leftovers.
for all I care
I don't care if (something happens). For all I care, the whole city council can go to the devil. They can all starve for all I care.
for all I, you, etc. ˈcare
(spoken) used to say that a person is not worried about or interested in what happens to somebody/something: I could be dead for all he cares!