my edit: 4x03

9

Hercule Poirot, a cinnamon roll

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Poirot & obsessive-compulsive disorder (OCD) 

Although Agatha Christie never called it by name, I think you could make a strong case for Poirot having a type of OCD. He shows signs of compulsion like arranging and repeated cleaning of items, as well as obsession with symmetry and exactness.