“Let’s do lunch” (meaning “let’s get together for lunch and discuss this”) was popularized from 1985 in the business speak of the entertainment industry in Los Angeles. The phrase quickly became overused and “Let’s do lunch—I’ll call you” became a way to brush someone off forever.
   
One citation of “let’s do lunch” exists from 1955, however, and is credited to “smart-talk boys…in the white-collar canyons of Manhattan.”
   
“Let’s do lunch…it’s on me” has become newly popularized as a saying on baby bibs.
 
 
The Free Dictionary
We(‘ll) have to do lunch sometime, and Let’s do lunch (sometime).
We must have lunch together sometime. (A vague statement that may lead to lunch plans.) Rachel: Nice to talk to you, Tom. We have to do lunch sometime. Tom: Yes, good to see you. I’ll give you a ring. Tom: Can’t talk to you now. Catch you later. Mary: We’ll have to do lunch sometime. John: Good to see you, Tom. Tom: Right. Let’s do lunch sometime. John: Good idea. I’ll call you. Mary: Catch you later. Sue: Sure. Let’s do lunch. Mary: Okay. Call me. Bye.
 
Urban Dictionary 
let’s do lunch
Hollywood slang for “You’re dead to me assface!”
“No really, I’ll call you! Hey let’s do lunch!”
by X-S Sep 2, 2004
     
buybuyBABY
Carter’s® “Let’s Do Lunch…It’s On Me” Bibs - Tan (3-Pack)
These adorable bibs in bright colors and patterns feature cute sayings. The waterproof inside protects baby while the fabric outside absorbs spills. 100% cotton. Machine wash. Imported. Package of 3 bibs.
   
Kohls.com
Carter’s® 3-pk. “Let’s Do Lunch” Feeding Bibs - Khaki
 
11 October 1955, Philadelphia (PA) Evening Bulletin:
IN THE white-collar canyons of Manhattan, the smart-talk boys are almost constantly “doing” some kind of “bit.” If they want to propose going to lunch, they day: “let’s do the lunch bit.”  If they see a motion picture, they “do the movie bit.”
     
29 April 1985, Los Angeles (CA) Times, “The Devil Is Making Me Do It” by Al Martinez, Metro, section 2, pg. 7:
From now on it would be, “Let’s do lunch sometime, have your girl call my girl.”
 
Google News Archive
29 July 1985, St. Petersburg (FL) Times, Pg. 2E, col. 5:
“Let’s do lunch sometime”
 
Google Books
28 July 1986, New York magazine, pg. 112, col. 1 classified ad:
Let’s Do Lunch—Midtown. He: 32. She: 25 plus/hungry.
 
Google Books
More of the Straight Dope
By Cecil Adams (Ed Zotti)
Edition: illustrated
Published by Ballantine Books, 1988
Pg. iv:
I love you, you’re beautiful, and let’s do lunch.
     
Google Books
Avenue of the Stars 
By Jina Bacarr and Ellis A. Cohen
New York, NY: Dutton
1990
Pg. 71:
Then he saw Alan Ladd Jr. “Laddie, let’s do lunch sometime soon,” he called out.
       
Google Books
How to Talk American: a guide to our native tongues
By Jim Crotty
Boston, MA: Houghton Mifflin Harcourt
1997
Pg. 163:
the L.A. farewell: a smile followed by:
. I’ll call you: “get lost, you’ll never hear from me again.”
. let’s do lunch: “I like you. but you’re a loser.”
   
news.com.au
Infuriating phrases jar language
By Angela Saurine
The Courier-Mail
October 13, 2008 12:01am
NEXT time you are at the pub and hear a glass smash, try to resist the urge to call out “taxi!”
 
If you want to catch up with a work contact, suggest something other than “let’s do lunch”.
 
And whatever you do don’t call someone to “touch base”.

That’s the verdict of fed-up Australians, who have voted on the most over-used and hated phrases in a nationwide survey.
 
(Trademark)
Word Mark LET’S DO LUNCH!
Goods and Services (ABANDONED) IC 016. US 037 038. G & S: AN ADVERTISING PUBLICATION DESIGNED FOR RESTRAUNT PROMOTION LETTERHEAD, BUSINESS CARDS, BROCHURES, ETC. FIRST USE: 19871201. FIRST USE IN COMMERCE: 19871201
Mark Drawing Code (5) WORDS, LETTERS, AND/OR NUMBERS IN STYLIZED FORM
Serial Number 73742548
Filing Date July 25, 1988
Current Filing Basis 1A
Original Filing Basis 1A
Owner (APPLICANT) HALL, HARRY THOMAS DBA AMERICAN ADVERTISING DIST. OF EASTERN ALLEGHENY INDIVIDUAL UNITED STATES 101 RODI RD. PITTSBURGH PENNSYLVANIA 15235
Type of Mark TRADEMARK
Register PRINCIPAL
Live/Dead Indicator DEAD
Abandonment Date April 27, 1989