“You had one job” is a caption frequently given on many images showing obvious fails.  There is a website of these images, titled “You Had One Job! Job related fails even kids can get right.” The saying is a joke, showing how people can mess up even one simple job.
   
On the television sitcom Friends, the episode “The One with the Sonogram at the End” that originally aired on September 29, 1994, Rachel (Jennifer Aniston) loses her engagement ring in the lasagna, and Monica (Courteney Cox) says, “I gave you one job!”
           
“You had one job. One job in the whole show. You had to lay a rope across the stage and you forgot” was a line in a 1995 play. “Oh leave it out! You tossers! You had one job to do!” was said by a character in the popular film Ocean’s Eleven (2001).
 
“Dude, you had one job ...” was printed in the Reno (NV) Gazette-Journal on February 18, 2007. “#youhadonejob” was posted on Twitter on June 27, 2010.
 
       
YouTube
Monica: I GAVE YOU ONE JOB
Apr 26, 2013
TV Shows
Monica: I GAVE YOU ONE JOB
S01 E02 Friends TV show 2
Show
Friends : The One with the Sonogram at the End
 
Google Books
Anne-Arky:
A Play in One Act
Toronto, ON: Theatrefolk
1995
By Lindsay Price
Pg. 25:
JULIE: You had one job. One job in the whole show. You had to lay a rope across the stage and you forgot.
 
IMDb (The Internet Movie Database)
Ocean’s Eleven (2001)
Quotes
[in a safe heist]
Basher: All right chaps. Hang on to your knickers.
[He triggers the bomb, and the safe door cracks open. Laughing, Basher dances into the vault - and the alarm goes off]
Basher: Oh leave it out! You tossers! You had one job to do!
   
18 September 2006, The Guardian (London, UK), “Golf: Ryder Cup countdown” by Lawrence Donegan, pg. 12:
Royal Lytham, 2001: Ian Woosnam, arms akimbo, looks to the sky in despair while a hollow-cheeked Myles Byrne stares at the ground, searching for a hole big enough to accommodate his shame in discovering an extra club in his boss’s bag. The penalty was two shots, and with it went the Welshman’s best chance of ever winning the Open Championship. “You had one job to do and you couldn’t get that right,” Woosnam told the bagman at the time - harsh, but the rest of the world was a lot harsher on Byrne, unfairly portraying him as someone so thick he couldn’t even count to 14.
     
18 February 2007, Reno (NV) Gazette-Journal, “Roundup, Part II: The Failure” by Cory Farley, pg. 9B, col. 6:
“Dude, you had one job ... .”
 
Twitter
Khristine Anderson‏
@khristine
..damn it, chicken pox vaccine! ..you had ONE job..
9:42 PM - 21 Sep 2008
 
Twitter
TJGoff‏
@TJGoff
By the way…to Justice Roberts messed up the oath, not President Obama.  You had one job today, John, one job!
11:53 AM - 20 Jan 2009
 
Twitter
Greg Allbright‏
@GregAllbright
hey Chief Justice Roberts, you had one job today..read a 35 word oath of office…5th graders are expected to memorize more
9:17 PM - 20 Jan 2009
 
Twitter
MV Beauty Lab‏
@mirandavoth
@ni_motjuste #youhadonejob #reffail
12:22 PM - 27 Jun 2010
 
Twitter
YouHadOneJob‏
@YouHadOneJob
“I had a dozen roses delivered to my mom today for her anniversary. They only delivered 11.” #youhadonejob
10:19 AM - 21 Jul 2010
 
You Had One Job!
September 13, 2012
THE NEW WHITE PEPPER THAT TASTES A LOT LIKE SALT
(Salt is shown in a pepper shaker.—ed.)
 
Know Your Meme
You Had One Job
Part of a series on FAIL / Epic Fail.
Updated 4 years ago by Don.
Added 4 years ago (2013—ed.) by ExudesAffluence.
About
“You Had One Job” is an expression used to call attention to perceived blunders made by individuals on the job. On the web, the phrase is heavily associated with FAIL image macros.
Origin
The earliest known mention of the phrase can be heard in a scene from the 2001 remake of the heist film Ocean’s Eleven, in which the character Basher Tarr (played by Don Cheadle) scolds his team for missing a step that singlehandedly leads to the failure of an otherwise well-planned vault heist (shown below).
 
[in a safe heist]
Basher: All right chaps. Hang on to your knickers.
[He triggers the bomb, and the safe door cracks open.]
[Laughing, Basher dances into the vault – and the alarm goes off]
Basher: Oh leave it out! You tossers! You had one job to do!
 
On April 25th, 2011, Redditor nomdeweb submitted a screen capture of a credit slide for the “Dinosaur Supervisor” in the 1993 film Jurassic Park, captioning the image with “You had one job in Jurassic Park. ONE JOB.” Prior to being archived, the post received over 8,100 up votes and 400 comments.
 
OCLC WorldCat record
You Had One Job, TSA… And You’re Failing
Author: Independent Voter Network
Edition/Format: Downloadable article Downloadable article : English
Publication: Independent Voter Network, (2015-06-09T00:15:57.000Z)
Database: ACI Scholarly Blog Index
Summary:
You Had One Job, TSA… And You’re FailingDepartment of Homeland Security Secretary Jeb Johnson reassigned the TSA’s acting director, Melvin Carraway, after the initial report was released. However, despite the agency’s alarming failures, President Obama continues to express confidence in its ability to keep the nation’s airports secure.Thomas A. HawkIVN.us - Independent Voter Network: Unfiltered News
   
OCLC WorldCat record
You had one job!
Author: Beverly L Jenkins
Publisher: Kansas City, Missouri : Andrews McMeel Publishing, [2016]
Edition/Format:   eBook : Document : English
Database: WorldCat
Summary:
If someone hangs a stop sign upside down or paints crooked lines on a highway, count on someone else to snap a photo and post it online. You Had One Job! is a collection of hilarious pictures features job-related disasters and general ineptitudes. All of these new, never-before-seen images will be accompanied by witty captions.