Used to address the end of the line in an escalated conversation, debate or exchange. A loss of temper or patience is often the catalyst.
Made famous by actor Christian Bale's infamous outburst on the set of Terminator Salvation.
"I think Sarah Palin got a bad rap in the press."
"Are you kidding?"
"Seriously, she's a terrific role model for women."
"We are done professionally."