A diner at a restaurant complains that the coffee tastes like mud. The waiter remarks: “It should be! It was ground this morning!”
     
This well-known coffee joke (a pun on the noun and the verb “ground”) dates to at least 1913.
   
 
4 January 1913, Cleveland (OH) Leader, “Funny Things You Hear at the Vaudeville,” Theatergoers,” pg. 8, col. 1:
“Waiter! This coffee is nothing but mud!”
“Yes, sir; certainly, sir. It was ground this morning.”
   
9 July 1913, Jackson (MI) Citizen Patriot, pg. 3, col. 5:
“Here, waiter, this coffee is like mud.”
“Yes, sir; it’s bound to be; it was ground this morning, sir.”
   
4 July 1914, Fort Wayne (IN) Sentinel, pg. 6, col. 7:
‘That coffee we had for breakfast was just like mud.”
“Well, what can you expect? It was only ground this morning.”
   
24 January 1918, Daily Kennebec Journal (Kennebec, ME), pg. 6, col. 4:
Waiter—The customers are complaining that the coffee tastes like mud.
Chef—That’s all right. Tell them it was ground this morning.—Tit-Bits.
 
Google Books
July 1918, The Bulltein of Pharmacy, pg. 41:
SCOUTMASTER: “This coffee tastes like mud.”
SCOUT: “Well, the kitchen squad said it was ground this morning.” — Boys’ Life.
     
Google Books
The Auto Era
By Winton Motor Carriage Co
v. 19 - 1919
Explained —
“Waiter, this coffee is nothing but mud.”
“Yes, sir, it was ground this morning.” — Voo Doo.
 
Google Books
October 1919, The Experimenter (Wellesley College), pg. 43:
“Waiter, this coffee is nothing but mud.”
“Yes, sir, it was ground this morning.” — The Voo Doo.
 
Google Books
September 1921, The Sptaula (a magazien for pharmacists), pg. 452, col. 2:
Diner: “Waiter, this coffee is nothing but mud.”
Waiter: “Yes, sir; it was ground this morning.”
 
Google News Archive
24 August 1927, Gridley (CA) Herald, pg. 4, col. 3:
Good Reason
Diner—What’s the matter with the coffee? It looks like mud.
Waiter—Well, sir, it was ground this morning.—Stray Stories.
   
5 August 1928, Chicago (IL) Daily Tribune, “The Best Joke I Ever Heard,” pg. F5:
Customer: “Thlis coffee tastes like mud.”
Walter: “Mud? Why that s probably because It was ground this morning.”
 
Google News Archive
20 June 1967, St. Petersburg (FL) Times, pg. 7D, cols. 3-4:
Husband: Did you know this coffee tastes like mud?
Wife: It was ground morning, dear.
 
Google Books
Jokes, Puns, and Riddles
By David Allen Clark and Lionel Kalish
Garden City, NY: Doubleday
1968
Pg. 196:
Diner: This coffee is like mud.
Waiter: Well, it was ground this morning!