Boomerang children refer to those young adults who choose to live with parents.
Dog in a manger refers to selfish person who has no consideration for others.
Last-ditch idea means the final proposal, after which there'll be no more.
To step up to the plate means to be able to deal with the difficult situation.
A trick question is asked in such a way that it easily misleads to a wrong answer.
"All very well, but" means something is good, but not good enough.
If something begins to wear thin, they are less effective due to overuse.
Doing something the hard way is to achieve one's aim through honest hard work.
To call someone's bluff is to point flat out that they are bragging.