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The warm and fuzzy feeling one gets after becoming ecologically enlightened; usually induced by listening to a ruddy south-westerner talk about off-the-grid construction, having an Australian permaculturist walking you through a food forest, or watching a Discovery Channel film about nature.

This is usually coupled with a gereric environmental-personal-responsibility lecture on the come-down when given by ecologically inclined scientists, often mistaken for global warming rhetoric by the less educated.
"I just had a greengasm after learning how to build an earthship from Dennis Weaver! It was great until he made me think about global warming..."

"That Audi commercial is like green-rape; I think I had a dirty greengasm after watching it. I have to go shower now."

"Geoff Lawton gave me multiple greengasms. I can't wait to watch that one again!"
by DeadJack March 20, 2010
The reaction an enviromentally friendly person has when they see/buy/hear about/do something good for planet Earth
They were selling recycled paper half price at WHSmiths; I had a greengasm
by wallpaperandglue November 23, 2010