The phrase is plastered on every printable surface and remixed hundreds of ways.
Bring it up in conversation with a Brit and you'll probably be met with an eye-roll - as noted in Fraser McAlpine's new book, "Stuff Brits Like."
But McAlpine, who lives in Cornwall, says the British secretly love the phrase because of its history.
Year: 1939
The phrase originated as a slogan in the spring before World War II. Anticipating the dark days ahead, the British government designed a poster to hang in areas being targeted by German bombers.
Around 2.5 million copies were printed, but not one of them was posted, as officials had last-minute doubts about whether the content was too patronizing or obvious. They also couldn't settle on an appropriate time to hang the posters. Save for a select few, the majority of the posters were destroyed.
Year: 2000
Fast-forward six decades and one of the remaining posters was discovered by a bookseller who bought a box of old books (where the poster was hidden) at auction. It was put up over the cash register in the seller's bookshop, Northumberland's Barter Books.
Pretty soon, customers were asking about where they could buy a similar poster, and the shop's owners, Stuart and Mary Manley, decided to print copies. Little did they know how fast the "Keep Calm" craze would spread.
Why Brits actually love the phrase
In his book, McAlpine breaks down the phrase, further explaining why the British have grown to love it.
There is something quintessential in the way the posters do not say "Don't Panic" or "We Will Prevail"... They say "Keep Calm," and what that means is, "We may be suffering something of an invasion at the moment, but that's no reason to start acting in a rash and hot-headed manner. We may be a subjugated nation - temporarily - but we are not about to start acting like savages."
And what of the "Carry On?"... As a nation, we have been trained to look past the bad behavior of our rudest guests, especially the uninvited ones, and rather than cause a scene, we shall just go about our daily business as if nothing has happened.
The slogan, in its purest form, is a symbol of nationalism. While the British may loathe its exploitation, they adore "Keep Calm" for its historical roots.