shit-eating grin

Etymology
Possibly from a contraction of "grinning like a ’possum eating shit", later detached from meaning and persisting due to its vividness (cf. "there are many ways to skin a cat" or "happy as a clam").

Noun

 * 1)  A broad smile indicating self-awareness that may suggest self-satisfaction, smugness, discomfort, or embarrassment.

Usage notes

 * The term is ambiguous and may indicate either a genuine broad smile (e.g. smug happiness) or a fake broad smile (e.g. trying to hide or get away with something).

Translations

 * French: rictus jubilatoire, sourire de faux-cul
 * Japanese: ドヤ顔


 * French: sourire à manger de la merde