“Before you give a colleague a piece of your mind, make sure you can spare it” is a jocular saying that has been cited in print since at least 2009. Other forms of the saying are much older. “Before giving any one a piece of your mind figure out whether you will have enough left to keep you going” was cited in print in 1913. “It never pays to give anyone a piece of your mind unless you have some to spare” was cited in 1926. “Before you give away a piece of your mind, be sure you have it to spare” was cited in 1930.
 
 
7 August 1913, Racine (WI) Journal-News, “Pert Paragraphs,” pg. 4, col. 6:
Before giving any one a piece of your mind figure out whether you will have enough left to keep you going.
 
15 December 1926, Marshall (MI) Evening Chronicle, pg. 1, col. 7:
SENTENCE SERMONS—By the REV. ROY L. SMITH
It Never Pays to Give—
(...)
Any one a piece of your mind unless you have some to spare.
 
10 April 1930, The Weekly Tribune (Moulton, IA), pg. 2, col. 3:
Before you give away a piece of your mind, be sure you have it to spare.
 
14 March 1957, Aberdeen (SD) American-News, “It Happened Last Night” by Earl Wilson, pg. 12, col. 5:
Advice our father taught us: When you’re about to give somebody a piece of your mind, be sure you can spare it.
 
24 May 1966, The Plain Dealer (Cleveland, OH), “Feminine Logic” by Jean Flynn, pg. 23, col. 2:
It’s fine to give someone a piece of your mind—but the question is, can you spare it?
 
Google News Archive
21 July 1991, Spartanburg (SC) Herald-Journal, “Sudden thoughts, second thoughts” by Bill Lyon, pg. D5, col. 4:
Before you give someone a piece of your mind, make sure you can spare it.
 
Google Groups: bit.listserv.christia
THOUGHT FOR THE DAY
Cindy K. Bannister
3/31/97
Before you give someone a piece of your mind - make sure you can spare it.
 
Google Books
7 Things He’ll Never Tell You:
. . . But You Need to Know
By Kevin Leman
Carol Stream, IL: Tyndale House Publishers, Inc.
2007
Pg. 174:
#2 Before you give your husband a piece of your mind, make sure you can spare it.
 
Twitter
Lisa Lomas
‏@lisalomas
Lisa RT @forces2 Before you give a colleague a piece of your mind, be sure you can spare it~~~funny. http://ff.im/-2LaP7
5:07 AM - 10 May 2009
 
Google Books
Protecting Clients from Fraud, Incompetence and Scams
By Lance Wallach
Hoboken, NJ: John Wiley & Sons, Inc.
2010
Pg. 90:
Profound Insight #8
Before you give a colleague a piece of your mind, be sure you can spare it.
 
Twitter
Cameron Morrissey
‏@ManagersDiary
DAILY WORK HUMOR - Before you give a colleague a piece of your mind, be sure you can spare it.
2:27 PM - 6 Apr 2014