A person who acts or thinks they're interested in purchasing a car that they can most likely not afford to buy. They spend a majority of their time trying to find things wrong with the car that's for sale by complaining the car is the wrong color,(when they knew that it was that color in the first place), its an automatic instead of a stick (but if it were a stick he'd want an automatic) or its missing a few features that they really wanted, like the irrelevant windshield washers on the headlights. Tire kickers generally low ball you on the first offer, just to see how desperate you are. They generally test your will to sell it to them by their indecision. Most tire kickers are indecisive car buyers who are cheapskates at heart, that will never fix the things or faults they find wrong on the car thats for sale if they buy it.
Tommy the tire kicker was testing Johns patience with the list of things he didn't like about the car.