1) Use a nail to poke holes in the eyes of the coconut. Drain the water into a blender.
2) Put the coconut in a pillowcase or some other heavy bag that won't rip. Slam it against concrete until the coconut breaks up into small pieces. Remove the hard shell and put the coconut meat into the blender with the water you drained from it. Blend until smooth, adding tap water if needed. This will be very thick, but makes an excellent base for smoothies.
SIDE NOTE: You can leave the light brown skin on the coconut meat. It doesn't change the taste at all, and if you take the time to remove all of it this recipe will take you forever to make.