coprophagous grin

A smug, self-satisfied, or overly pleased smile, especially one that (intentionally or unintentionally) irritates others. A humorous literalization of the phrase "shit-eating grin" (where coprophagia, or coprophagy, means the ingestion of feces). She's been walking around with that coprophagous grin on her face ever since she found out she got into Harvard. I really wanted to wipe that coprophagous grin off his face after he won the poker game. A: "What's up with the coprophagous grin?" B: "Oh, nothing. Just that Jenny—that's right, the most popular girl in school—said she'd go to prom with me."