There’s a popular weight loss joke:

“To lose weight, go to a paint store. You can get thinner there.”

“Sign in paint store: Want to get thinner? Try ours—98c a gallon” was cited in 1964. “All they have to do is go to a paint store. You can get thinner there” was cited in 1971.


Google Books
Freedom and Union
Volumes 19-21
1964
Pg. 60:
Sign in paint store: Want to get thinner? Try ours—98c a gallon.

Google News Archive
9 July 1971, Milwaukee (WI) Sentinel, Alex Thien column, pt. 1, pg. 21, col. 1:
Bill Ambrosh has come up with a system for people who want to lose weight. All they have to do is go to a paint store. You can get thinner there.

5 August 1979, Richmond (VA) Times-Dispatch, “The National Challenge” edited by J. Baxter Newgate, pg. M-6, col. 3:
The results of National Challenge No. 129, in which you were to invent a novel way to lose weight.
(...)
Second prize:
Go to a paint store. You can get thinner there.
-- Deana Marie Cherrico,
Camp Springs, Md.

Google Books
More Bulletin Board-Ers
By Helen Eisenberg and Larry Eisenberg
Lima, OH: CSS Publishing Company, Inc.
1984
Pg. 69:
If too fat, get thinner at paint store.

Google Books
Diabetes Cookbook for Dummies
By Alan L. Rubin, Fran Stach and Denise C. Sharf
Foster City, CA: IDG Books Worldwide
2000
Pg. 21:
And don’t go to a paint store and expect to get thinner.

Twitter
Kristin Finley
‏@kristinfinley
On a diet? Go to the paint store. You can get thinner there. #punday
2:30 PM - 12 Apr 2009

Google Books
Kevin Ahern’s 1001 Punniest Limericks
By Kevin Ahern
Lulu Publishing (Lulu.com)
2014
Pg. 38:
The overweight man couldn’t bear
Each diet led him to despair
So he raced to the door
Of the nearest paint store
When he heard you could get thinner there.