I have been looking for parking so long I could have walked

On Calle Loiza a man leaned out of his car window and called to a friend on the pavement, "I have been looking for parking so long I could have walked from home." The friend said, "Then park on the next block, you are already here." "That is the next block's problem," he said, and drove on. I laughed. I do not yet understand the unwritten rules about which spaces are fair game, and nobody has offered to explain.