Definition of that's done it! in US English:

that's done it!

phrase

informal
  • Used to express dismay or anger when something has gone wrong.

    • ‘‘That's done it!’ said a growl from the crackling intercom system. ‘Our energy transfer unit just had a stroke.’’
    • ‘‘Uh oh, that's done it,’ he said. ‘We've got to get off this ship ASAP!’’
    • ‘Oh hell, that's done it.’