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I'm a member of Greenpeace and I just helped poison a dog.
— Peter · Nobody's Fool

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker places a declared affiliation beside an action that seems to contradict it. Helping poison a dog makes the mention of Greenpeace sound painfully out of place. The humour lies in that abrupt clash between how someone identifies themselves and what they have just done.
Context reviewed