1
Means the person doesn't care at all and would rather poop in your shoes than deal with whatever is happening.
I give 0 fucks about this test. I'm going to fail and eat my lunch in the hallway.
I give 0 fucks if the teacher gives me detention. I'll just sleep through the next class.
I give 0 fucks about the mess in my room. It's a warzone and I'm the general.