adverb, noun or participle which takes 'suru'
Describes someone silently showing a bad mood, often with a pouting or sulky expression. Can be used adverbially or with する to mean 'to sulk'.
See also: ブスッと
彼はムスッとして、何も言わなかった。
He sulked and didn't say anything.
妹は叱られてムスッとしている。
My younger sister is in a huff after being scolded.