give (one) up as a bad job
To cease trying to get one to change because it seems like a futile task. Just give him up as a bad job—you'll never get him to be the responsible man you're looking for.
give somebody/something up as a bad ˈjob
(informal) decide that it is impossible to do something or to change somebody and then stop trying to do it: ‘Are you still studying Japanese?’ ‘No, I gave it up as a bad job. It was far too difficult for me!’