expression, na-adjective
sour expression; looking disgusted
Describes a facial expression of extreme displeasure, as if one had bitten into something bitter. Often used with verbs like する or 顔をする.
See also: 苦虫
彼は苦虫を噛み潰したような顔で、その話を聞いていた。
He listened to the story with a sour expression on his face.
上司に叱られて、苦虫を噛み潰したようだった。
After being scolded by his boss, he looked thoroughly disgusted.
Literally 'as if having chewed up a bitter bug'. The phrase evokes the involuntary grimace one would make when tasting something extremely bitter, and is used idiomatically to describe a sour or disgusted facial expression.