CHICAGO » Score one for number 2.

Burger King — always the bridesmaid, never the bride — delivered a rare jolt of publicity for itself by calling for a “ceasefire” with historic archrival McDonald’s in full-page ads Wednesday in the Chicago Tribune and The New York Times.

In “an open letter,” Burger King implored McDonald’s to collaborate on creating the stuff of fast food junkies’ dreams: the McWhopper. The idea was to come together in Atlanta — a midpoint between Burger King’s Miami headquarters and McDonald’s, based in suburban Chicago — and make the sandwich at a pop-up restaurant for one day in promotion of the global Peace Day on Sept. 21.

In a Facebook post, McDonald’s CEO Steve Easterbrook said: “We love the intention but think our two brands could do something bigger to make a difference.”

Commence the social media backlash from people who apparently really liked the McWhopper idea.

“It’s a great move by Burger King. It’s a win-win for them. You can’t lose,” said Dan Azzaro, senior lecturer in the advertising program at DePaul University College of Communication. “It’s all about ‘How do you agitate the giant?’”

The “burger war” between McDonald’s and Burger King is a thing of the past, Azzaro said, but Burger King’s McWhopper proposal relies on that very premise. In reality, McDonald’s is more challenged these days by fast casual restaurants like Chipotle and Panera Bread, he said.

“We’re talking about Burger King. And how often do we do that except for when that creepy King rolls around?” Azzaro said, referring to the Burger King mascot.

Azzaro said Easterbrook’s response was “very corporate” and “kind of cold,” though it did leave open the possibility of some sort of brand collaboration for a higher cause.

“Now the ball’s in McDonald’s court to do something big and fun,” Azzaro said.

Alexander Chernev, marketing professor at Northwestern University’s Kellogg School of Management, said Burger King’s proposal put McDonald’s in a tough spot. If it had agreed to the McWhopper, customers would come to think of the Whopper and the Big Mac as more or less the same, he said, which isn’t good for the brand.

“In people’s minds, it would have lasted much longer (than one day),” Chernev said.

Chernev disagreed that it was now incumbent on McDonald’s to come up with a bolder concept for Peace Day. After all, social media reaction is a fickle beast.

“Whether they’ll do something for Peace Day or not, I’m not sure people will even remember it a week from now,” Chernev said.

Maybe not, but the conversation is certainly good for Peace Day, said Jeremy Gilley, founder of the British nonprofit Peace One Day that promotes the annual event. In 2001, the United Nations adopted the day as the International Day of Peace. But chances are, many Americans just learned about it on Wednesday.

“Here’s a day of peace being talked about because a corporation made a move,” Gilley said. “That can only be a good thing.”