When he didn't get the pay raise he was expecting, he had to take another job to 'pick up the slack'. [=to make up for the money he was not making]
The manager has to 'take up the slack' when employees don't do their jobs correctly.
We left some 'slack' in the budget so that we can hire more people if we have to.
(..) Look, you can't... The knight is here. Excuse me. Don't I know you... Plain lo, in the morning Lola in slacks. Lois Lane. Mmm. Come see the view. Now, the secret is the height. It's the building material. (..)2016 Batman v Superman: Dawn of Justice