expression, godan verb (-su)
get jealous; show jealousy
Idiomatic expression referring specifically to a woman's jealousy. The literal meaning is 'to grow horns', which is a metaphor for jealousy.
See also: 角を生やす
彼女は彼が他の女性と話すとすぐに角を出す。
She gets jealous as soon as he talks to another woman.
あの人は嫉妬深くて、よく角を出す。
That person is very jealous and often shows it.