Someone who uses the environment in a destructive fashion purely for their own gratification without regard for the common good of life on earth. These people have no sense of remorse or guilt or remorse about their destructive impact on the environment. Ecopathism is a personality disorder much like sociopathism.
Even though Bill knows that driving his SUV by himself and keeping his heat at 75 F in the winter is very wasteful and bad for the environment, he doesn't care, and doesn't feel any guilt, therefor he is an ecopath.
A person so obsessed with "environmentalism" and "being green" that they deem any sort of infraction against their misguided mindset as the ultimate sin. Possessed of a gigantic "holier than thou" attitude. Were this type of person given a choice between cutting down a tree and strangling a newborn baby...well, sorry baby!
-"Man, that guy just gave me the dirtiest look when I threw my water bottle into the garbage!"
-"Kyle? Yeah, don't mind him. He's a total fuckin' wingnut ecopath"