Masked men robbed a branch of fast food outlet McDonald's at gunpoint in Meyzieu, near Lyon, in eastern France on December 27.
A video circulating on social media and verified by Euronews shows two men wearing tracksuits and masks entering the restaurant around 22:00 CET and snatching the cash registers.
As one of the robbers points his weapon at an employee yelling "open the register", some of whom continue to eat as if nothing is the matter.
"I feel like they were amateurs because of the way they spoke to each other. They had no plan B or C," the author of the video told Le Parisien newspaper.
"I'm traumatised, I have nightmares. It's too hard, I don't wish this on anyone," he went on, adding that "McDo and me, it's over now."
The restaurant reopened its doors as usual on December 28 while police have launched an investigation.
In a statement to Euronews, McDonald's said that it will support the authorities' probe and that management "immediately set up a support unit for the employees present during the robbery on Friday December 27 and wishes to salute their exemplary composure".