Yes, you would say "I won't give a shit", if referring to a future event which would not matter to you. You would say "I don't give a shit", when referring to a present event which doesn't matter to you.

you can say that but most English speakers say " I don't give a shit" ^^

You can say this, but it is more natural to say "I don't give a shit."

U can say whatever u wanna say bro haha

Yes, you would say "I won't give a shit", if referring to a future event which would not matter to you. You would say "I don't give a shit", when referring to a present event which doesn't matter to you.