idioms

a fly on the wall (an unnoticed observer or listener) I wish I could be a fly on the wall during the negotiations. You should be a fly on the wall to hear what he is saying about you.   fly on the wall – English Vocabulary

a dead duck  informal (an unsuccessful or useless thing, a failure) The project was a dead duck right from the start. (a person who is in great trouble) If Dad finds out what you did, you’ll be a dead duck.   dead duck – English Vocabulary

a cold fish (an unfriendly and unfeeling person) He rarely talks to the others. He’s a cold fish. He never helps his mother clean the house; he is a cold fish.   cold fish – English Vocabulary

  a chicken and egg situation (said when it is difficult to tell which one of two things was the cause of the other) You need experience to get a job, but you need a job to get experience. It’s a chicken-and-egg situation.   chicken and egg – English Vocabulary

a good egg (a nice person) He is such a good egg that everyone wants to be his friend. He is a good egg, and I’m sure that he will lend you some money.   good egg – English Vocabulary