A ping pong ball would not fit down the filler neck of a gas tank for any car made before 1973. Before 1973, car gas tanks were wide upon from the filler cap to the tank. After that time the tanks were changed so they wouldn't accommodate the nozzle that was designed to pump regular (leaded) gasoline. The device at the top of the tank allows the unleaded nozzle but is too small for a ping pong ball to pass. To get something that big into a gas tank would take some major work that could not be accomplished in a parking lot.
When Detectives Goren and Eames arrest Kieth in the bar they don't actually handcuff him, as they are walking away he is just holding the cuffs with his hand.