If you have a friend who tells you to cock your pistol, it means that whatever your fried is about to tel you, will surprise you to no end. Based on the television shows on which it appeared in the 1950s, it appears to be a Southern American expression, most likely from Tennessee.
When “I Love Lucy” was running on television, every once in a while a recognized celebrity would be written into the storyline. In the 1954 episode entitled, “Tennessee Ernie Hangs On” scripted-cousin Tennessee Ernie Ford turned to Lucy and said:
Cock your pistol,’cause you ain’t gonna believe this no how!
The expression wasn’t the first time a musician had used it. In fact, two decades earlier,in 1933, the expression found it’s way into the title of a country blues song entitled, “You May Cock Your Pistol In My Face But You Ain’t Done Nothing To Me” and sung by Memphis Minnie.
In 1909, P.W. Joyce compiled a book of Irish folk songs entitled, “Old Irish Folk Music and Songs.” One of the songs was an Irish jig that went by the name of “Cock Your Pistol, Charlie.” It’s been said that P.W. Joyce learned the piece as a child in County Limerick, sometime before 1850.
At some point, however, to cock your pistol referred to a variant of the “pipers’ grip” when playing an Irish whistle (also known as an Irish flute). There didn’t appear to be only one accepted way of holding a flute. There appears to have been, however, methods to establish what was best for each musician, to fit the flute to their unique physical conformation and them to the flute.
In 1802, Publisher C. Roworth, Hudson’s Court, Strand published a book by Charles James entitled, “A New and Enlarged Military Dictionary, or Alphabetical Explanation of Technical Terms: Containing, Among Other Matter, A Succinct Account Of The Different Systems of Fortification, Tactics, etc.” The subtitle continued with “Also The Various French Phrases and Words That Have An Immediate or Relative Connection with the British Service, or May Tend to Give General Information on Military Subjects in Either Language.” That’s quite the title for a book, wouldn’t you say?
In Mr. James’ book, under the heading cock your pistol the following is found on the page with the subject line “PIS – PIT” and reads as follows:
Drop the pistol into the left hand, cocking with the thumb of the right, and as soon as done come to the second position, viz. muzzle upwards.
It appears that the expression transformed from its literal meaning in 1802 into a term referring to how one should hold an Irish whistle, and some time in the 20th century, it transformed once more into an expression of anticipated surprise.
Historically Speaking 