Nuance Dictionary / Interpersonal Friction
삐치다 (삐지다) ppi-chi-da (ppi-ji-da)
To sulk, pout, and act mildly upset (often passively)
A very common behavior in relationships. If you forget an anniversary, your partner won't necessarily scream; they will give you short answers, avoid eye contact, and cross their arms. They have '삐쳤다'.