It happened in Snodhurst Avenue, Chatham, when he met a man pretended to be interested in buying a sofa.
Instead, he jumped in the Mercedes advertising the sofa for sale and sped off.
The victim's foot was injured when the thief ran into him as he escaped.
The carjacking happened at about 3.15pm yesterday.
A Medway Police spokesman said: "Officers are investigating a report of a vehicle theft from an address in Chatham.
"It is reported that a man arranged to view the sofa which had been advertised for sale, but then drove off in the car.
"He is described as being an Asian man, 25 to 30-years-old, 32ft 40in and of extremely large build.
"The owner was not seriously hurt, he had some bruising to his foot but didn’t require medical attention."
