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.
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."
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."
That was an awesome 1-up about his mom. You totally green mushroom'd him!