Once a marine, always a marine.

A trio of would-be robbers had to learn that the hard way after they targeted the wrong service station in Yuma County, Arizona.

Deputies said an armed suspect came into the store and pointed his gun toward the cashier.

Little did the suspect know the customer next to him was a former U.S. Marine and was about to foil their plans.

“The Marine Corps taught me not to [mess] around,” the customer told authorities after quickly disarming the robber in Arizona.

CCTV from inside the station shows the moment the quick-thinking marine drops his keys and suddenly disarms the gunman before pinning him to the ground.

The other two suspects fled the scene after seeing the Marine take down the suspect.

Extracted in full from: Wild moment brave customer takes on gunman in botched petrol station robbery | 7NEWS