Part of the classic 'three wise monkeys' set (see/hear/speak no evil) rooted in a centuries-old Japanese proverb (originally tied to the Tลshล-gลซ shrine's carving) about avoiding exposure to bad influence. Today it's used far more casually for 'I didn't see anything' plausible deniability or covering one's eyes at something awkward or scandalous.
Keywords: embarrassed, evil, face, forbidden, forgot, gesture, hide, monkey, no, omg, prohibited, scared, secret, smh, watch