Mug, snout, fat face, trap; a huge, chubby, or smug face. Derived from the dialectal and low-colloquial verb рядиться (to dress up, to adorn oneself), which historically shifted from describing someone over-dressed or made-up to mockingly focusing on a large, prominent, or overfed face. In everyday street, youth, and low-colloquial slang, it is a highly expressive and derogatory noun for a human face, specifically one that is notably wide, chubby, or bloated (наел себе ряху — “he grew himself a fat mug”). It is often used to imply greed, smugness, or excessive weight, similar to “snout” or “pie-hole” (ну и ряха у него — “look at the size of that guy’s mug”).
Азиат не ответил, только щекастой ряхой помотал.
The Asian didn’t respond, just wiggled his cheeky mug.
(Борис Акунин, Любовник смерти, 2001)
