People who believe that others are motivated purely by self-interest and lack sincere motives, or members of the ancient Greek Cynic philosophical school.
From Greek 'kynikos' (dog-like, from 'kyon' meaning dog), named after their founder Diogenes who lived like a dog to demonstrate self-sufficiency. The school got its name because members rejected social conventions.
It's wild that 'cynic' comes from 'dog'—the Cynic philosophers literally chose to live like dogs, sleeping in barrels and owning nothing, to prove humans don't need society's comforts to be happy.
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