on/at the Greek calends 永不
A: Tom borrowed money from me yesterday.
B: What? Why did you lend money to him?
A: What's wrong? He said he would pay back tomorrow.
B: Pay back! Yeah, he will pay back on the Greek calends.
A: Oh, my God! Really?
B: He never pays his debts off. so nobody here lends a penny to him.
A: I see. I won't do such a thing again.