Piece of cake
Something very easy
Catch someone red-handed
To find someone doing something wrong.
Give someone the cold shoulder
to ignore someone
Spill the beans
Reveal a secret.
Hit the nail on the head
To be exactly right about something.
Bite the bullet
To endure a difficult situation bravely.
Once in a blue moon
Very rarely
Raining cats and dogs
Raining very heavily
Fish out of water
Feeling uncomfortable or out of place.
Pull someone's leg
To joke with someone by teasing them.
Under the weather
Feeling slightly ill.