I don't remember the numbers, but Donald Shoup has demonstrated that a fairly large amount of gas is used (wasted) by people cruising around as they look for a good parking spot.

Along with a long line of cars, I was recently held up by somebody in a car, blocking the lane while waiting for another car to vacate a diagonal parking space. There was another space just three slots down. This driver was holding up seven or eight other people in order to shorten his own walk to the store by 15 steps. If that isn't smug, I don't know what is.