Parking has been called third rail of local politics, and for good reason. At a panel Wednesday on "Getting Parking Right," Nelson\Nygaard transportation planner Jeff Tumlin put it this way: "People hate the existing system, but they'll also hate any changes you make to the rules. No matter what you do, people are going to be very upset with you." Sam Zimbabwe, planning director for the District Department of Transportation, was also on the panel. From the look on his face, he knows that has his work cut out for him as the agency tries to bring some measure of rationality to the city's tangle of parking regulations. We all want to be able to park wherever we want, for as long as we want, and we want it to be free. But we might as well wish for a world of free and infinitely available ice cream. We can't have it, and we give up a lot by trying to get there.