Yabai

Originally meant "dangerous" or "sketchy" — and it still can. But starting in the 1990s, young people began using it for positive things too, like "amazing" or "incredible." Now it is basically the Swiss Army knife of Japanese slang. Depending on context, it can mean "dangerous," "awesome," "delicious," "cute," "terrible," or just about anything that provokes a strong reaction. Probably the very first slang word foreigners pick up in Japan because you hear it constantly. The short form "やばっ" (yaba) is used as a quick exclamation.