Regrettable
Frustrating, Vexing, Disappointing
い adjective
The kanji is regret and this is regrettable. And something regrettable is likely to be frustrating, vexing, or disappointing.
悔しい generally expresses a feeling of frustration, regret, or vexation, often due to a sense of failure or missed opportunity. It conveys a strong emotional response to a situation where one feels disappointed or bitter about not achieving something they desired, especially when they were close to success or when the outcome feels unfair.
It's regrettable if you're not cool, yah (くや)? Yah, that would be pretty vexing.
他の人が日本語で何を話しているのか理解できない時、私はいつも悔しい思いをします。
I always think it’s frustrating when I can’t understand what the other people are saying in Japanese.