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A marijuana addict, a stoner, a pothead. "Grass" is a well-known term for marijuana.
Curious George always wondered what the Man in the Yellow Hat has been smoking lately that smelled so good. And so George then sneaked into a weed cabinet which the Man in the Yellow Hat has left unattended, grabbed a few J's and a lighter and then started enjoying himself. He could not stop afterwards. What a grass monkey he now is!

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Mark H. Proud Urban Dictionary author since February 2004.
by Mark H October 01, 2005
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3
A ghetto drank. Made by filling a cup half full with Busch Light. Then you peel a fresh orange. Squeeze the orange into the drank. After the orange is fully squeezed pour the rest of the Busch Light into the cup. Drink the Grass Monkey.
A Grass Monkey is Busch Light filled with a squeezed orange.
by Bunty n KMac May 04, 2008
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4
Small monkeys that eat baby kittens. They hide in the grass and are invisible to the naked eye.
Mommy my kitten is being attacked by Grass Monkeys!!!
by Grandmaster January 12, 2004
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