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Hold the pickle, please. McDonald's has declined Burger King's proposal to collaborate on a "McWhopper" for world peace.

The "McWhopper" would have combined elements of the chains' famous "Big Mac" and "Whopper" burgers to create a new double-decker burger. The burgers would have been sold for one day in a franchise jointly run by employees of both companies.

Burger King is tying the publicity stunt to a nonprofit called Peace One Day, which says it promotes Peace Day. The United Nations created the International Day of Peace in 1981 to coincide with its annual opening session in September. It then designated Sept. 21 as the annual "day of non-violence and cease-fire" in 2001.

Burger King touted the idea in full page ads in the New York Times, social media, and a taste test on the TODAY show.

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But apparently they didn't ring anyone over at the Golden Arches first.

"We love the intention but think our two brands could do something bigger to make a difference," read a post on McDonald's Facebook signed by McDonald's CEO Steve Easterbrook.

But Easterbrook chided Burger King for using the language of battle to describe their competition, saying it paled compared to the "real pain and suffering of war."

"A simple phone call will do next time," read a testy postscript.

Burger King has struggled against number one McDonald's for a few years. A new owner has cut costs and only recently started to raise sales.

As the underdog, it's very cost-effective to take shots at the big cheese, said marketing expert Martin Lindstrom, author of the forthcoming book, "Small Data." And in coming across as high and mighty, McDonald's handed Burger King a victory.

"McDonald’s could easily have reacted in a fun, cheeky and engaging way - turning the entire situation around. Yet they missed this opportunity," he wrote in an email. "1:0 to Burger King."

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