Yabai (やばい)

One of the most useful and vague Japanese slang, yabai. It has so many meanings like very good, very bad, cute, dangerous, cool, cheesy, scary, great, ... It can express that someone is impressed by something, but that’s all. We can't know the details only from this word.
もっとも便利で曖昧な日本語スラングの一つ、 やばい。この単語にはすごくいい、すごく悪い、かわいい、危ない、かっこいい、ださい、怖い、すばらしい、……などなどたくさんの意味があります。この単語は誰かが何かに感動したことは表せますが、それだけです。この単語だけでは詳細を知ることはできません。

This is a real example of conversation between a high school girl and me.

Me: 「どうやばかったの?」
Girl: "Uh, yesterday I went to a yabai movie theater, there were like yabai people, the movie was yabai and I was really yabai!"
Me: "How yabai was it?"

It’s like a joke, but Japanese young people so often use this word for real.

Yabai is simple and easy to say, so that recently older people, not only young people, tend to use it easily. But I think it's not that good to use this word. If you are used to using this word, it stops the increase of your vocabulary because you can express almost every feeling with just using it. It would also cause you to not think about things deeply or carefully. However, Japanese people tend to use it more and more.

I worry about Japan‘s future... In Japanese, 日本の未来、超やばい (Japan's future is super yabai)。