“If you hang out in a barbershop long enough, you’re going to get a haircut” is a saying used by Alcoholics Anonymous and similar recovery programs. If you hang around alcoholics (or a bar, for example), you’re going to take a drink. “A favorite saying of old-timers in Alcoholics Anonymous is, ‘If you hang around the barbershop long enough, you’re going to get a haircut’” was cited in Charles W. Crewe’s A Look at Relapse (1974).
 
Another barbershop proverb is “Never ask a barber if he thinks you need a haircut.”
   
 
Google Books
A Look at Relapse
By Charles W. Crewe
Center City, MN: Hazelden
1974
Pg. 65:
A favorite saying of old-timers in Alcoholics Anonymous is, “If you hang around the barbershop long enough, you’re going to get a haircut.”
 
Google Books
From Liquor and Loneliness to Love and Laughter
By Dean Marr
Kansas City, MO: Sheed Andrews and McMeel
1978
Pg. 139:
One of the old-timers snapped, “If you hang around a barber shop long enough, you’re going to need a haircut!”
 
26 January 1983, Boston (MA) Herald,  “Inside the NBA” by Peter Vecsey, pg. 70, col. 6:
“I’m never gonna do drugs again,” Drew (Utah Jazz basketball forward John Drew—ed.) vows. “Or hang around people who use them. If you hang around a barber shop long enough, you’re going to get a haircut.”
 
Google Books
The Bullpen:
Gateway to the State Prison
By Julio Lao
Bloomington, IN: AuthorHouse
2006
Pg. 57:
As one popular saying goes, “if you hung out in the barbershop long enough, you would eventually get a haircut.” Parker hung around with his buddies who did drugs and it did not take long for him to do the same.
 
Yahoo! Voices
If You Stay in the Barbershop Long Enough, You’re Bound to Get Your Hair Cut
craig cavallo, Yahoo! Contributor Network
Jul 21, 2008
There is a deli on 58th and 7th.
     
Urban Dictionary
hang around the barbershop
To put oneself in situations where undesirable consequences may likely unfold, especially regarding persons trying to break a bad habit.
Stems from the adage “If you hang around the barbershop, you’re bound to get a haircut.”
John continued to sit with the smokers during break time even though he knew it was risky to hang around the barbershop.
#barber#shop#relapse#hazardous#dangerous
by brianbbad September 22, 2010
 
Google Books
Still Standing:
Addicts Talk About Living Sober
By Bucky Sinister
San Francisco, CA: Conari Press
2011
Pg. 144:
If you hang out in a barbershop long enough, you’re going to get a haircut: This saying drives me nuts. Mainly because you’re going to get a haircut eventually whether you hang out in the barbershop or not. It’s said in relation to who you’re spending your time with or where you hang out.