adverb taking the 'to' particle, adverb, noun or participle which takes 'suru'
sullenly; taciturnly; gloomily
Describes a person's silent, gloomy, or uncommunicative manner. Often used with する or と to describe behavior or expression.
彼はむっつりと座って何も言わなかった。
He sat there sullenly and said nothing.
むっつりした顔で部屋を出ていった。
He left the room with a gloomy look on his face.
noun
taciturn person; uncommunicative person
Refers to a person who is habitually silent and uncommunicative. Often used in a slightly negative or critical way.
あの人はむっつりで、あまり話さない。
That person is taciturn and doesn't talk much.