Eco-sinner has two meanings. An accidental Eco-sinner is someone who desecrates the environment without meaning to because they are uneducated about what the impact they have on the planet is. An intentional Eco-sinner is a person who is highly educated on pollution but loves pollution and hates the environment, going out of their way to pollute because they enjoy something within pollution such as the look of it or its impact on the environment. They aren't sadists but will knowingly do things like littering and pouring chemicals on the ground. The term Eco-sinner goes back to the books Confessions of an Eco-Sinner by Brad Pearce, and No Place for Eco-Sinners by Racheal Bates.
She's such an Eco-sinner, she poured bleach on the grass just because she wanted to pollute the earth!
He's an Eco-sinner but he has no idea that he should be recycling his cans, not throwing them in the garbage.