Great for teaching idioms :)

1. have a monkey on your back = To have an addiction, especially
a drug addiction; To have a deep, uncontrollable desire to
something such as Gamble, Smoke, Sweet or Drink.

2. It's raining cats and dogs= It’s pouring with rain/It’s raining
very heavily.

3. Big fish in a small pond = A big fish in a small pond is an
important person in a small place or organisation.

5. the green-eyed-monster = a feeling of anger or unhappiness
because somebody you like or love is showing interest in somebody
else; jealousy;

6. Rat race= A fierce, competitive struggle for power, position.

7. pull a rabbit out of the hat ( informal )=suddenly produce
something as a solution to a problem; to do something very clever
and unexpected that solves a problem.