ムキになる

expression, godan verb (-ru)

get worked up; take something too seriously; get huffy

Describes someone who becomes overly serious, irritated, or angry in response to a joke, teasing, or trivial matter. Often used when someone can't take a lighthearted comment and reacts defensively.

• ちょっとからかっただけなのに、すぐムキになるんだから。

  I was just teasing a little, but you immediately get all worked up.

• 彼かれは負まけず嫌ぎらいで、ゲームに負まけるとムキになる。

  He hates losing and gets seriously worked up when he loses a game.