A person who has 'gone green', and is now highly judgmental of all others who they feel are not 'green enough'.
Can be accentuated when the individual does not have a well rounded knowledge of the actual issues of climate change.
Bob traded in his SUV to buy a Hybrid, then when he saw me drive in to work in my gas car he gave me the stink eye and hasn't talked to me since. Little does he know that my small car still gets better gas millage than his Hybrid, and has for the last ten years. What a greenneck.