1. He is a sick dancer
When somebody says you are sick or that is so sick, don’t be hurry to fight back. Nowadays, the youngsters like to use negative adjective to exaggeratedly express a positive admire or surprise. Thus, it depends on the situation.
It could mean you are really ill, sometimes it means you are far from normal.
What are you doing? You must be sick.
Sometimes it could be totally opposite meaning, like very good,
Oh my gosh, that’s so sick. I am so touching!
Sometimes it means immersing in something positive.
You are a sick dancer, aren’t you.