APAD: Blow the gaff

Meaning:

   To make public a secret or reveal a plot.

 

Background:

   When someone is said to blow the gaff it is usually when exposing some crime

   or underworld activity. It's the kind of expression you might expect to hear

   James Cagney use in some mobster film.

 

   ...

 

   The first printed example that I know of is from 1819, in James Vaux's

   A Vocabulary of the Flash Language, the first dictionary ever compiled in

   Australia from The Memoirs of James Hardy Vaux, 1819.

 

     BLOW THE GAFF, a person having any secret in his possession, or a knowledge

     of any thing injurious to another, when at last induced from revenge, or

     other motive, to tell it openly to the world and expose him publicly, is

     then said to have blown the gaff upon him.

 

   Vaux was British by birth and was well acquainted with the language of the

   criminal classes. He was an inveterate thief and swindler and was transported

   to Australia as a convict in 1801.

 

- www.phrases.org.uk [edited]

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The end of the third week of June, Bill took the east-bound local train to the

port city to pass the College English Test level 4, a pre-requisite for college

graduation, for his best bud.

 

That muggy overcast morning, he showed up taut, wooden, and on an empty stomach

(He always skipped breakfast on a test day) at the classroom entrance where the

three dozens of exam sitters were verified. A first-time ringer, he didn't try

hard to relax. They were supposed to fret and the last thing he wanted was to

stand out like a sore thumb by appearing too tense or lax. His palms started to

sweat as he handed in his student ID booklet and his heart missed a beat or two

as the rheumy eyes of the 50-ish woman behind a pair of rimless glasses darted

from his face to his mugshot and back. It was not until they started working on

the problems before he could ease up.

 

In the next two hours had the proctors taken a closer look at the partial

embossed chop over the right bottom corner of his photo, they would've noticed

its poor quality. They might have suspected, double-checked, blown the gaff on

the spot, and both Bill and his chum would've been expelled from uni.