A person who insists on one-upping you everytime.
Derived from Mario Bro's -1up
Person A: "I sprained my ankle the other day."
Person B: "Yeah well I broke my ankle once and got the flu. Plus I haven't slept in 48 hours. I'm so tired."
Person A: "You're such a Green Mushroom, Nick."
by Meish September 29, 2008
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As in the Mario series when one gains a green mushroom the words "one up" flash on the screen, this is when you tell a story and someone else tries to tell a story better than you.
John: "i once skydived"

Bob: "yeah well i skydived and shot 4 ninjas whilst slaying a dragon and throwing the ring into Mt. Doom."

John: "Green Mushroom me again and you die."
by jameswilson December 22, 2009
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Something one says when is given an unexcpected bonus.
Joerge not only gave me his stereo, but 5 CDs as well. So that was a big green mushroom.
by Miyamoto October 10, 2005
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In an exchange of burns and insults, dealing a comeback better than the previous diss.
That was an awesome 1-up about his mom. You totally green mushroom'd him!
by placatedmayhem June 8, 2007
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Apparently it's what System of a Down likes on their pizza.
From SOAD's "Chic 'n' Stu"

What a splendid pie,
Pizza-pizza pie,
Every minute, every second,
Buy, buy, buy, buy, buy,
What a splendid pie,
Pizza-pizza pie,
Every minute, every second,
Buy, buy, buy, buy, buy,

pepperoni and green peppers, mushrooms, olives, chives
pepperoni and green peppers, mushrooms, olives, chives
by viva riolu May 7, 2011
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