What a lot of teenagers say when they're annoyed or mad with someone, especially when someone corrects their spelling, or as they incorrectly like to refer to it as: grammar.
I don't give a fuck, or "no fuck were given" meant you didn't care, but it has turned into a forced insult. Althought teenager may say "You can correct my grammar all you want, because obviously I don't give a fuck" they obviously care about having something they wrote corrected.
You can do whatever you want, I don't give a fuck. I have better things to do.