I admire this youtube channel for providing a lot of info on how to speak French, but just recently I was talking with my teacher and she said that I said something weirdly. We were supposed to pretend a conversation in a train. My friend and I were talking. He said:
- Le voyage a Paris, c'est long, hein?
- Grave! - I replied
And then my teacher was confused, because she said grave meant generally "heavy" and has no use in a sentence I wanted to use. She has also never heard of using "genre!" in order to express disagreeing. So... Is it a French slang? How do these words actually work?