don’t give up the day job—is used to humorously tell a person that he could not do smth. professionally:
- Your English is fine for getting by in a conversation, but as for writing English (far less translating): don’t give up the day job.
Note: The expression does not correlate in meaning with the phrase don’t give up the ship—used to tell a person not to surrender and keep on trying or working on smth. till he gets it right:
- Keep up the good work and don’t give up the ship, just yet. There is light at the end of the tunnel!
give something up as a bad job—stop doing smth. because one does not feel it is worth continuing; acknowledge that one has no hope of success:
- I tried to make him see things as I did, but when this effort failed, I gave it up as a bad job.