As a Verb or Adjective:
1. To say no to something, to not accept something, or to get rid of something because you do not like it at all; to dismiss, reject or discard something. English = reject, dismiss.
2. To refuse to do something or to stop doing something because you think it is silly, unimportant, too difficult or a waste of time.
3. To give up on doing something because you think it is too difficult or because you really do not want to do it at all. English = give up. Idiomatic English = throw in the towel.
1. Used alone to mean that you do not care about or for something in the slightest. English = 'I couldn't care less!', 'It means nothing to me!'
2. Used alone to mean that you are stopping doing something because you have had enough of it or it is difficult and you are not happy. English = 'Stuff it!', 'Enough is enough!', 'I'm tired of it!', 'I've had enough!'