1. Apples And Oranges

Apples and oranges refers to two incommensurable items, i.e. a comparison of things that cannot be compared. Though they are both fruits, apples and oranges are separated by color, taste, juiciness, uses and so forth.

The idiom first appeared as apples and oysters in John Ray’s 1670 “Handbook Of Proverbs.” Equivalent terms exist in many languages, from “grandmothers and toads” in Serbian to “love and the eye of an axe” in Argentine Spanish.
 

*An idiom is an expression whose meaning is not predictable from the usual meanings of its constituent elements, such as “kick the bucket” or “hang one’s head.’”

It’s not so easy to make a pie, but anyone can eat one. “As easy as pie” is an idiom used to describe a task or experience as pleasurable and simple—like the act of consuming a pie, not the more difficult task of baking one.

According to Wikipedia, the phrase was used in 1910 by Zane Grey in “The Young Forester” and in 1913 “The Saturday Evening Post.” It is probably a development of the phrase “like eating pie,” first recorded in “Sporting Life” in 1886. The phrase is often interchanged with “piece of cake,” which shares the same connotation.
3. Cup Of Tea

Popularized in British Edwardian slang, “cup of tea” originally referred to something pleasant or agreeable. The negative usage, as in “not my cup of tea,” arose during World War II as a more polite way to say that you didn’t like something.

“You don’t say someone gives you a pain in the neck,” explained journalist Alister Cooke in his 1944 Letter from America. “You just remark, he’s not my cup of tea.’”

“In a nutshell” refers to a short description, or a story told in no more words than can physically fit in the shell of a nut.

The ancient Roman encyclopaedist Pliny the Elder claimed that a copy of Homer’s “The Iliad” existed that was small enough to fit inside a walnut shell. Almost 2,000 years later, in the early 1700s, the Bishop of Avranches in France tested Pliny’s theory by writing out the epic in tiny handwriting on a walnut-sized piece of paper.

Lo and behold, it fit!

5. Walking on Eggshells

This phrase means taking great care not to upset someone. It is thought to have originated in politics: Diplomats were described as having the remarkable ability to tread so lightly around difficult situations, as though they were walking on eggshells.

So go ahead and spill the beans—it’s just like apples and oranges.