It's means that once you had interest about something or someone but now you have lost it... you are over it. You don't care anymore, that thing doesn't affect you the way it did before... in a good or bad way... YOU ARE OVER IT. Actually, it depends on the context but that's the general meaning...

means you don't give a hoot :P

It means you had done with it and don't care about it anymore. You don't turn back. :)

it means I don't care about it anymore

Means I donot care anymore.