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1.
A former gamer's username. This gamer briefly went through a lot of FPS's. And when I mean briefly, I mean in about a week. Such as Jedi Knight : Jedi Academy, Quake 3, Counter Strike 1.6, Unreal Tournament 2004, etc... He "owned" as some gamers said at each game. Now the word has been sometimes used in replacement of the words "pwn" , "uber" and "ownage" in video games.

Because of the previous definition I mentioned. People have started using this word more often. So people now are using this new definition for it. "A sheep that vomits". That simple. But people don't really "enjoy" this type of sheep, so it has been known as the least favorite kind.
"That guy just green sheeped you in Quake 3"

"I hate green sheep. Their messes are so disgusting"
by plazity March 28, 2007
 
2.
A term used to describe fans of a CFL team called The Saskatchewan Roughriders. Roughrider fans are known to dress in all green during football games and are collectively known to worship their only major league sports team as though it were a God or religion. Most, if not all, Roughrider fans are blind, staunch supporters of their team even when the team has the worst standings in the league...this is largely due to their boredom, as there is little else to do in Saskatchewan but drink and dress in green.
The green sheep weeped when the Roughriders lost.
by MrRados November 21, 2010