Do not try to open a coconut by whacking it with a hammer. A surprising amount of strength paired with uncommon delicacy of aim are necessary here. Attempting this method without that fine balance can result in a unique pattern of divots in the deck and an unscathed coconut.
Do not try to open a coconut to make a sauce via a sledgehammer, either. Flying coconut shell shards have been known to take out an eye.
Do not try to open a coconut with the Civil War saber that you found in the house you are renting for the week.
Do not try to open a coconut by dropping it from the roof. If your roof is high enough for this to work, you really shouldn’t be crawling around up there clutching a coconut in one hand. Also, the amount of alcohol that you drank to make this seem like a good idea in the first place is always contraindicated when dealing with a coconut or a roof.
Do not try to open a coconut to make a curry by playing baseball with it. It doesn’t yield much usable flesh or juice or a long enough game. Same goes for croquet.
Finally, the machete. If you actually own a machete, I assume you know how to wield it. Feel free to do so. As for the rest of us, I absolutely do not recommend swinging any heavy, sharp bladed instrument at a spherical, impermeable nut. Don’t say I didn’t warn you.
Really, the only way I have come upon to satisfactorily open a coconut is to travel to Thailand (or Costa Rica or Mexico) and wait for the man walking up the beach with a net full of coconuts swung over his back. Pay him some fraction of a dollar to chop it with his handy blade and hand you the perfect seaside sipper in about 10 seconds.
For those of you real go-getters out there, here are a few links: http://www.wikihow.com/Open-a-Coconut