“You know what I mean, jelly bean?” is a rhyming slang phrase that was used in the teen talk of the 1940s and 1950s. “What you mean, jelly bean?” was cited in an August 1944 newspaper. “What d’ya mean, jelly bean?” was printed in a syndicated column in September 1944. “Do you know what I mean, jellybean?” was cited in a 1954 newspaper.
 
“YKWIMJB?  You know what I mean…Jelly Bean…” was posted on the newsgroup misc.health.alternative on February 11, 2003.
   
   
18 August 1944, Pittsburgh (PA) Post-Gazette, “Junior Commandos,” pg. 21, col. 6:
It goes like this: What you mean, jelly bean? What I said, pun;kin head. Don’t hand me that line, Frankenstein. You’re like a bear, you never get anywhere.
 
17 September 1944, The Sunday Star (Indianapolis, IN), “Tricks for Teens” by Nancy Pepper, pt. 4, pg. 11, col. 3:
RHYME TIME—“How’s the weather, heather?” is the way you’re making with the poetry. Here’s a gem that doesn’t make any sense, but it’s typical of your rhymes without reason.
 
What d’ya mean, jelly bean?
What I said, cabbage head.
It doesn’t rhyme, Frankenstein.
Yes, it do, Fu Manchu.
Don’t get hot, coffeepot.
Don’t get mad, Alan Ladd.
 
Oh, brother—we can read the words but they don’t make sense!
 
26 November 1944, Boston (MA) Sunday Globe, “Tricks for Teens” by Nancy Pepper, comics sec. pg. 5, col. 5:
Rhyme Time—“How’s the Weather, Heatter?” is the way you’re making with the poetry. Here’s a gem that doesn’t make any sense, but it’s typical of your rhymes without reason.
 
What d’ya mean, Jelly Bean?
What I said, Cabbage Head.
It doesn’t rhyme, Frankenstein.
Yes, it do, Fu Manchu.
Don’t get hot, Coffeepot.
Don’t get mad, Alan Ladd.
 
O, brother—we can read the words but they don’t make sense!
 
3 October 1945, The Oregonian “Young Oregonians: English Tough, That’s No Bluff” by Aquilla Jackson, pg. 13, col. 7:
Masculine: I see what you mean, Jellybean. Feminine: I see what you mean, Madame Queen.
 
13 August 1950, The Atlanta Journal and The Atlanta Constitution (Atlanta, GA), “If You Want To Be A Winner, ‘Cat Around’” by Alice Richards, pg. 18-F, col. 3:
If you describe some unattractive girl as a “beast,” a cat will reply, “I see what you mean, jellybean.”
 
28 February 1954, The Sunday Star (Washington, DC), “Do Kids Speak English?” by Beulah Racklin, This Week magazine, pg. 28, col. 3:
Rhyming expressions, which are mainly for effect rather than to convey any actual meaning, are very popular and somewhat confusing like ‘Do you know what I mean, jellybean?’ ...
   
Google Groups: misc.health.alternative
A Liberal Hoax Turns Out to Be True
DEBBEE1023
2/11/03
(...)
You must have had a sheltered life growing up….YKWIMJB?
 
JB stands for Jelly Bean…..what’s so bigoted about that?
 
YKWIMJB?  You know what I mean…Jelly Bean…
 
Twitter
😎Mondo Coolio 😎‏
@CheVolay
It was disappointing to see that YKWIMJB was not in the list for Twitter abbreviations.
You Know What I Mean Jelly Bean.
12:18 PM - 27 Oct 2009
 
Twitter
jnet‏
@jeannbeann_
You know what I mean jellybean. #YKWIMJB
12:28 AM - 21 Sep 2012