Similes!
Clear as mud
Very unclear or confusing
Heart of Gold
Someone good and kind
Sleep like a ___
Log
Piece of cake
Super easy
Cool as a Cucumber
Super chill, not worried
Bent out of shape
Mouse
In hot water
In trouble
Like a bull in a China shop
Very clumsy
Hit the books
Study a lot
Fish out of ____
Water
Out of the blue
All of a sudden
Out like a light
Fast asleep
I am under the weather
I'm sick
I could eat a ____
horse
Let the cat out of the bag
Tell secrets
Avoid like the plague
Stay away
He's an open book
A person who is easy to understand and doesn't hide their feelings or thoughts
Blind as a ____
Bat
My dogs are barking
My legs hurt