Using a SHARP knife, cut both ends off the grapefruit, make sure to get to the "meat". Then holding it sort of on edge, start at the top and cut down around to the bottom. This takes a tiny bit of practice, but isn't difficult.
Continue on around...
...until you have a nekkid grapefruit! If there is still the white rind left on in a few places, it's ok but you can go back and slice that off. Sharp knives are a MUST in the kitchen!!
Pro chefs then slice each segment out, and it's not hard - just loses some of the nice juice. So I separate each segment one at a time, and peel the membrane off - it is pretty easy.