“Master debater” is often said with a wink, clearly hinting at the word “masturbator.” It’s not known exactly when the double entendre began.
 
The Los Angeles (CA) Times reported on March 4, 1990 about the American television sitcom Doctor Doctor:
 
“In this same episode, Frewer’s character tries to cheer up his partner’s son after a frustrating school debate by telling him, ‘Debaters get all the chicks.’ On a subsequent take he punctuated the line with: ‘Especially master debaters.’”
   
“He (G. Gordon Liddy) calls himself a ‘master debater and cunning linguist’” was published in a 1994 book.
 
 
Los Angeles (CA) Times
Never Ready for Prime Time? : ‘Doctor, Doctor’ is the latest wild and crazy comedy to find the going tough on network TV
March 04, 1990 | STEVE WEINSTEIN
(...)
During the last several months, “Doctor, Doctor” and its star, Matt Frewer (of “Max Headroom” fame), have tried to straddle the perilous fence that separates successful mainstream TV sitcoms and the handful of nutty, demented comedy series that break with the medium’s familiar formulas but leave behind a large part of the audience in the process.
(...)
In this same episode, Frewer’s character tries to cheer up his partner’s son after a frustrating school debate by telling him, “Debaters get all the chicks.” On a subsequent take he punctuated the line with: “Especially master debaters.”
   
29 October 1994, The Economist, “The Colorado governor’s race: Sex, booze and anti-incumbency.” pg. 28:
Making things worse, after a handful of debates in which Mr Romer had got the better of his opponent, Mr Benson abruptly admitted as much, dropping out of the eight remaining contests and sending the governor a trophy declaring him a “master debater”.
 
Google Books
A River Lost:
The Life and Death of the Columbia
By Blaine Harden
New York, NY: W.W. Norton & Company
1996
Pg. 50:
McDowell told me that Liddy is “a pretty interesting fella. You know that when he was a kid, he cooked a rat and ate it. He has a lot of humor on the show. He calls himself a ‘master debater and cunning linguist.’
   
Urban Dictionary
master debater
A term to refer to someone who is kicking your ass in a debate because you have no intelligent rebuttal.
The term is effective because it sounds like masterbater.
Sam: Actually, a recent poll of climatologists indicates that a vast majority—not a fringe minority—is concerned about global warming.
Jim: Sam, you’re a master debater.
by AbnormalBoy October 13, 2004
 
Twitter
Can This Change
‏@canthischange
you may be a cunning linguist but i’m a master debater
2:00 AM - 16 Dec 2007
   
Google Books
(If everyone is a writer or artist, then) everyone is also an auto mechanic
By Marijke De Roover
Lulu Publishing (Lulu.com)
2014
Pg. ?:
“Well, you might be a cunning linguist, but I am a master debater.”
 
Twitter
Christopher Feehan
‏@CJFeeh
One thing no one can deny about this debate and all of Trump’s debates:
He’s a master debater. (Just love that old joke)
7:44 PM - 26 Sep 2016
 
Twitter
joelle
‏@joelle_webber
*mr Roda talking about the debate*
“obviously Hillary won that last night because Trump isn’t a master debater..Nvm that didnt sound right”
1:30 PM - 27 Sep 2016