The 28-year-old was shot in the shoulder in the eastern suburb of Noisy-le-Grand on Friday evening.
Ambulance crews battled to save the waiter at the small cafe on the outskirts of Paris but he died at the scene.
The unhappy customer allegedly lost his temper because his sandwich was not made quickly enough, according to Le Parisien.
Local residents were left shocked by the incident, with one asking: “He was killed for a sandwich?”
A 29-year-old woman told French media: “It is sad. It’s a quiet restaurant, without any problems. It just opened a few months ago.”
But others noted a rise in drug dealing and public drunkenness in the area.
Police have launched a murder investigation and a manhunt for the gunman who fled the scene.