before you could say Jack Robinson

before (one) can say Jack Robinson

Quickly or suddenly. (The true identity of Jack Robinson is unknown.) I'm not far from your house, so I'll be there before you can say Jack Robinson.
See also: before, can, jack, Robinson, say

before you could say Jack Robinson

OLD-FASHIONED
COMMON If you say that something happened before you could say Jack Robinson, you mean it happened very suddenly and quickly. The pair of them were out of the door and down the steps before you could say Jack Robinson. Note: People sometimes change Jack Robinson to a word or expression that relates to the subject they are talking about. She was on the phone to New York before you could say long-distance. Note: The identity of Jack Robinson is unknown and the name might have become popular because both elements were once extremely common. The phrase appears in the novel `Evelina' (1778) by Fanny Burney: `I'll do it as soon as say Jack Robinson'.
See also: before, could, jack, Robinson, say
References in classic literature ?
Why," said he, "a magician could call up a lot of genies, and they would hash you up like nothing before you could say Jack Robinson.
And before you could say Jack Robinson he had whipped out a whacking great revolver
Before you could say Jack Robinson, we had two Christian Churches in Britain -- and it was a bit of a mess-up .
BEFORE you could say Jack Robinson, a young golfer by the same name had won the regional rounds of the Golden Putter Competition and is heading for the national finals at Wentworth in July as North West Champion.