Today’s Japanese slang word is 激ヤバ (“gekiyaba”). 激 means violent or intense, and ヤバ comes from やばい, slang for dangerous, terrible, cool, etc. So, “really bad” or “really good”, depending on the context.

The specific context I found it in was the phrase “激ヤバ援交”, with 援交 (“enkou”) abbreviated from the well-known 援助交際 “enjo kousai” (paid dating, also known as “schoolgirl prostitution”). A quick search on Amazon Japan suggests that in sexual contexts, gekiyaba means “extreme”. So, either the young lady in question was willing to do more than usual, or the resulting video had little or no censorship, or perhaps both.