It could not be learned which of the two men was stabbed.
Authorities were called to the restaurant in the 6200 block of Livingston Road in the Oxon Hill area about 7 p.m. after a fight was reported. The fight spilled outside the restaurant where the stabbing occurred.
The victim was described as a resident of the Washington area. He was taken to a hospital, where he died less than an hour after the dispute broke out, Donelan said.
The Popeyes chicken sandwich was highly popular this summer, with a sales volume that caused the chain to exhaust its initial inventory by late August.
Donelan said police are looking for the assailant and called on him to turn himself in.
“For you to get that angry over anything; for that type of anger to develop into this type of violence . . . is a very sad and tragic day,” Donelan said.