Feeling frustrated or irritated because things are not going as one wishes; a vexing, impatient feeling.
テストで答えがわかっているのに書けなくて歯がゆい。
It's frustrating when I know the answer on the test but can't write it down.
部下の成長が遅くて上司として歯がゆい思いをしている。
As a boss I'm frustrated because my subordinate's progress is slow.
操作方法がわからず、歯痒い気持ちで説明書を何度も読んだ。
Not knowing how to operate it, I read the manual repeatedly with a vexed feeling.