“I beat a black belt at karate. My next opponent is a green sock”

To face “a black belt at karate” usually means facing “a person with a black belt,” but a joke is:
 
“I beat a black belt at karate. My next opponent is a green sock.”
 
The joke was posted on Twitter on January 15, 2016.
 
     
Twitter
nick
@ApexMasta
I beat a black belt at karate.
My next opponent is a green sock.
6:53 PM - 15 Jan 2016
   
Twitter
Church Jokes
@ChurchJokes
I beat a black belt at karate.
My next opponent? A green sock.
9:38 AM - 16 Jan 2016
   
Twitter
LaffGaff
@LaffGaff
I beat a black belt at karate today. .
My next opponent is a green sock.
#funny #jokes #jokeoftheday
5:12 PM - 19 Jan 2016
       
Twitter
Anon
@twitface27
I beat up a black belt in karate last evening… my opponent for this evening will be a red sock…
11:52 PM - 4 Feb 2016
 
Google Books
3000 Jokes, 2997 Laughs
By Mike Haskins
London, UK: Portico
2017
Pg. ?:
I beat a black belt at Karate yesterday. My next opponent will be a green sock.
   
Twitter
Jaeden Genesee
@Safari_Street
Today, I beat a black belt at karate.
My next opponent is a green sock.
10:36 PM - 29 Nov 2017
 
Reddit—Jokes
I beat a black belt at karate
submitted April 17, 2018 by Shortty10
My next opponent is a red sock