高端黑 (gao duan hei)
This is not an actual chinese phrase but is instead an internet slang.
It refers to SARCASM. Yes, it is the Mandarin Chinese equivalent of sarcasm.
To explain it, it is referred to when someone uses a humorous and witty way to reply which may appear to be positive but is actually to make fun of, and ridicule.
An example of how you can use it:
"看完这部电影，其实给五分是高端黑。可以说黑的漂亮！"
(kan wan zhe bu dian ying, qi shi gei wu fen shi gao duan hei. ke yi shuo hei de piao liang)
This sentence is translated as "After watching this movie, giving it 5 points is to be sarcastic. You can say this is pretty 'black'"