In a ballsy bit of fast food schadenfreude, Burger King is now selling Whoppers for a penny.

The catch? You have to download their Burger King app — at any location of their golden arch enemy: McDonald’s.

Yep, passive-aggressive patty peddling is a new marketing technique of choice for drive-thru mega-chains.

How this flame-grilled burn works: Burger King geofenced McDonald’s franchises nationwide — allowing the app to track when customers are at the Big Mac competitor, which in turn unlocks the penny Whopper deal.

After placing orders via the app, customers are “detoured” to the nearest Burger King to fetch the spoils of this fast-food war. If you want one, you better hurry; the deal only works once and ends Dec. 12.

Mickey D’s can’t be happy about being trolled this way, especially after making headlines last week when an investigation turned up traces of poop on a number of McDonald’s touch-screen kiosks.

According to Thrillist.com, McDonald’s has yet to weigh in on whether they think Burger King’s Whopper Detour gimmick is a bunch of crap.

Something tells us Ronald McDonald is worried about his royal reign being challenged: Nasdaq has reported that the average royalty revenue per McDonald’s franchise is significantly higher compared to Burger King, since the former “serves more customers per restaurant, given its higher market share.”