A man managed to fight off a pistol-wielding thug with a jar of instant coffee during an attempted car-jacking.

The victim, known only as Jason stopped to buy the Nescafe Blend 43 and cigarettes at service station in Frankston, Melbourne on Tuesday night.

The thief demanded Jason hand over the keys to his Mercedes but the 48-year-old fought back, swinging at him with the jar and kicking him.

'He had a handgun there and he pointed it at me and he said 'give me your f***ing keys,' the Melbourne man told 7 News.

When he refused, Jason was struck over the head and fell to the ground.

His fresh jar of Nescafé Blend 43 smashed, allowing him to use the shards of glass to fight off the attacker.