Something not probable to happen
When pigs fly
Agree with someone
See eye to eye
Say the truth, tell a secret...
Spill the tea / beans
Be very expensive
Cost an arm and a leg
The last thing to happen before getting angry
The last straw
Be easy
Be a piece of cake
Go to Sleep
Hit the sack
Stop doing something
Call it a day
I'm a little bit ill
I'm a little bit under the weather
Good luck!
Break a leg!