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One of the Holy Grail sexual acts. This involves one man and three women. The lucky man will have one woman on his penis and one hand in each of the other two women. This makes him look like Neptune's tri-pronged trident.

And like everything nautical, the whole thing smells of fish and is very slippery.
Nick: "I scored big the other day, I hit on three chicks and they did Neptune's trident with me."
Dude: "Way to go my man! You IS a sex god!"
by Wizards Sleeve May 07, 2007
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