Idioms can be classified into several categories, based on the comparison used in the idiom, like animal idioms, colours idioms, sports idioms etc.
1. Animal idioms:
At a snail's pace
Fish out of the water
2. Sports idioms:
Give it your best shot
The ball is in your court
3. Food idioms:
A piece of cake
Food idioms - based on food items:
- A hard nut to crack - A difficult problem to solve.
- A piece of cake - Very easy thing to do.
- Couch potatoes - Lazy person who refuses even to move.
- Bread and butter - Basic necessities.
- In a soup/pickle - In a difficult situation.
- Like two peas in a pod - Always together.
- Not my cup of tea - Not my usual type.
- To butter up someone - Flatter someone.
- To spill the beans - Reveal a secret.
- You can't have your cake and eat it too - You can't have something in two ways, choose one.
Sports idioms - based on sports terms:
- The ball is in your court - The decision is yours.
- Give it your best shot - Make the best attempt.
- Front runner - The person most likely to win.
- Out of someone’s league - Not at a level where one is as good as someone else.
- Hat trick - Being victorious three times in a row.
Animal idioms - based on animals:
- Let the cat out of the bag - Reveal a secret.
- Lion's share - The biggest share.
- Wild goose chase - On a pursuit of something not about to be fruitful.
- Fish out of water - In an uncomfortable place.
- Kill two birds with one stone - Get two things done at the same time.
Colours idioms - based on colours:
- Gray area - Something which does not have clear specified rules.
- Green with envy - Extremely jealous.
- Once in a blue moon - Very rare occasion.
- White lies - Harmless, innocent lies.
- Black sheep - Odd person or bad person in the group.