“400” or “Four-hundred” (chocolate milk)

 
Soda fountain slang (also called “diner slang” or “restuarant slang” or “hash house Greek”) is mostly of historical interest today. A numerical list:
 
5 (five)—large glass of milk
10 (ten)—root beer
13 (thirteen)—the boss is around—watch out
14 (fourteen)—special order
19 (nineteen)—banana split
21 (twenty-one)—limeade
21 (twenty-one)—a customer who doesn’t tip
21 (twenty-one)—two of an item for the same person or table
31 (thirty-one)—lemonade
41 (forty-one)—orangeade
44 (forty-four)—coffee
51 (fifty-one)—hot chocolate
55 (fifty-five)—root beer
71 (seventy-one)—a cup of coffee
72 (seventy-two)—two cups of coffee
81 (eighty-one)—a glass of water
86 (eighty-six)—all out of an item)
87 1/2 (eighty-seven-and-a-half—a good looking customer
88 (eighty-eight)—customer is waiting for the check
89 (eighty-nine)—a movie star is in the store
90 (ninety)—a pretty girl has arrived
91 (ninety-one)—English muffin
91 (ninety-one)—seltzer
95 (ninety-five)—a customer who walks out without paying
97 (ninety-seen)—vegetable soup
98 (ninety-eight)—assistant manager
99 (ninety-nine)—manager
99 (ninety-nine)—an exceptionally pretty girl has arrived
400 (four hundred)—chocolate milk
 
 
Newspapers.com
26 October 1937, Stuart (FL) Daily News, “Ye Editor’s Easy Chair,” pg. 2, col. 1:
“Four hundred.” (Chocolate milk).