Good luck with that*

Used when you believe that someone is doomed to fail and their efforts are fruitless.

“You think you can just walk into Pilkington’s office and convince him to move the deadline? Good luck with that.”

*Some common phrases may be used in a sarcastic way. It’s usually the context (or/and intonation) that gives away what the speaker actually means. Sarcastic words are not to be interpreted literally; they convey the opposite meaning of what seems to be said.