First used in Kurt Vonnegut's book, Breakfast of Champions, this phrase means roughly, "to take a leak."

"Sometimes somebody would say in his presence, 'Excuse me, I have to take a leak.' This was a way of saying that the speaker intended to drain liquid wastes from his body through a valve in his lower abdomen.

And Trout would reply waggishly, 'Where I come from, that means you're about to steal a mirror.'"
Guys, I'll be back in a second. I've gotta go steal a mirror.
by j0hnb0n April 9, 2007
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First used by Kurt Vonnegut's character Trout in the novel, Breakfast of Champions. It means to take a leak.
by j0hnb0n April 12, 2007
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