Regrettable, Vexing, Annoying
い adjective
The kanji is regret and this is regrettable. Could also be vexing or annoying as well.
くやしい
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.