What is a cliché?
A cliché is an overwrought phrase, like "it's raining cats and dogs" or "scared to death." At one time those phrases were unique and original but over time, well, they lost their original luster, and people just kinda keep using 'em. Clichés are the spam of language. Spam. Spam. Spam.
Why do we use clichés?
I could be cute and populate this post with overwrought clichés, but I am not. We use clichés, or stock phrases because we don't know what else to say. Instead of thinking through how we want to say something, we pull from the storehouse of ready-made phrases.
Clichés are like Hallmark cards for languages. Instead of coming up with a clever way to say good morning, we use a hallmark cliché, "What's up?"
Two decent examples
When was the last time you used the expression, "it's raining cats and dogs"? Did you notice when you said it you probably had no idea to why or how the expression "cats and dogs" has anything to do with rain? If you don't know the logic behind an expression then it's a sure sign it's cliché. She flew out of the office like a "bat out of hell" would be a nice simile if it hadn't been used ad infinitum since the first bat actually did fly out of hell - whenever that was.
Why Are Clichés So Horrifying?
Because clichés enervate language. That's why.
Cliché as Euphemism
At a funeral we might use a form of cliché called euphemism (worn out phrases used to mollify a situation or thought) say, "She's in heaven now," or "I'm sorry for your loss" instead of saying something poignantly creative, we use stock phrases so we don't have to think or feel. "Euphemism" is from the Greek for "good word" but I'd say, the best word is the one you articulate yourself, no matter how hokey.
Mad Magazine and Cliché
Growing up, I learned about clichés not from a grammar teacher, but from Mad Magazine. Paul Coker occasionally did a column for MAD called "Horrifying Clichés."
He would take a couple of stock phrases and draw what they would look like as monsters.
It was one of those MAD columns that were funny but educated in some weird MAD way. I'm sure the Usual Gang of Idiots approved because I think the column became popular. There are several anthologies of his work, like this one, The Mad Monster Book of Horrifying Clichés.
image credit: "Trying to get rid of the sniffles" by Paul Coker, Jr.