“Brain surgery” is used in an idiom that means “a complex subject.” “It’s not brain surgery” is a popular saying; a later saying is “it’s not rocket science.”
   
“This was a football game, not brain surgery” was cited in print in 1969.
 
“It can be like rocket surgery at times”—a blend of “rocket science” and “brain surgery”—was cited in 1997.
 
 
23 November 1969, San Diego (CA) Union, San Diego (A) Union, “Coaching Over, Gilllman Learns World Is A Fascinating Place” by Jack Murphy, pg. H-1, col. 1:
This was a football game, not brain surgery, and Gillman was pretty exercised at times.
 
6 December 1969, Lima (OH) News, “Letterbox,” pg. 19, col. 4:
The teachers are singing the old “underpaid” song again. Teaching is an honorable, useful and necessary profession, but it isn’t brain surgery.
(Letter from Norman Findley.—ed.)
 
31 October 1972, Omaha (NE) World-Herald, “Trevino Quitting Fractures Image” by Jim Murray, pg. 22, col. 1:
It is not the purpose of this article to suggest golf is easy money. Putting for a living is a hard way to make a buck. But it ain’t brain surgery either.
 
Google Books
Everything a Woman Needs to Know to Get Paid What She’s Worth
By Caroline Bird
New York, NY: Bantam Books
1974
Pg. 101:
“It isn’t brain surgery, I told my mother.”
 
Google BOoks
Tribute
By Bernard Slade
Garden City, NY: Nelson Doubleday
1978
Pg. 34:
Well, I know it’s not brain surgery, son — but it has its moments.
 
22 December 1985, Sunday Intelligencer (Doylestown, PA), “David Shula? He deserves a shot at coach” by Phil Sheridan,  pg. B-6, col. 3:
Football is a game. No one is suggesting that 26-year-old David Shula rule the universe. That’s a job for someone a little older. But coaching football is not rocket science and it’s not brain surgery. It’s a game, nothing more, no matter what anyone says.
 
Google Groups: comp.os.linux.misc
Win32 (was Re: stop complaining! MS Windows rules!)
David F. Skoll
10/25/97
(...)
> It can be like rocket surgery at times, but if you know how to use it
> it’s quite powerful.
 
“Rocket Surgery?”  You mean “Brain surgery.”  Or “Rocket science.” 😊
 
Urban Dictionary
rocket surgery
(n.) a play on words which mixes two common metaphors: “rocket science” and “brain surgery”
(...)
by fugitive247 November 07, 2004
   
OCLC WorldCat record
It’s not brain surgery : simple tips to getting a grip on a more successful life
Author: Kimberly Alyn
Publisher: West Conshohocken, Pa. : Infinity Publishing, ©2006.
Edition/Format:   Print book : English