Place the avocado on a work surface. Make a lengthwise cut, slicing until the blade hits the pit. Hold the knife steady and rotate the avocado, cutting around the pit.
Pick up the fruit and give it a twist. The two halves should come right apart.
Pick up the half with the pit in it. Carefully whack the knife into the pit, then twist and lift it out. Pop off the pit by scraping the edge of the knife on the trash can or sink.