shape up or ship out

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shape up or ship out

1. (idiomatic) To either improve one's behavior or else be required to leave; to either improve one's performance in an activity or else withdraw from that activity completely.
   • 1978 April 3, R. Z. Sheppard, "The Far Side of Friendship (review of Scott and Ernest by Matthew J. Bruccoli)," Time:

     Portions of those letters quoted by Bruccoli indicate that though Hemingway could be sympathetic, he used a lot of ink telling Fitzgerald to shape up or ship out.

• Often expressed in the imperative mood, as in an ultimatum such as:

  This is your final warning! Shape up or ship out!

• shit or get off the pot