Peel grapefruit with a sharp knife, removing all peel and white pith. Working over a medium bowl, cut the segments from the surrounding membranes and let them drop into the bowl. Squeeze the peels and membranes over bowl to extract all the juice before discarding them. Halve, peel and pitavocado. Cuth lenghtwise into 1/4 inch thick slices, then cut the slices in half. Gently stir the avocado and pomegranate seeds into the grapefruti mixture.