“Hot diggety dog” (or “hot diggity dog” or “hot dickety dog,” among other spellings) is a slang extension of “hot dog.” Frequently, the “dog” is left out of the phrase and a person exclaims “Hot diggity!” The (now dated) slang expression indicates excitement.
 
“Hot diggety dog” probably was influenced by the nursery rhyme “Hickory Dickory Dock.” Several early spellings were “hot dickety dog.” with “dickety” resembling “dickory.”
 
The first citation of “hod diggetty” is recorded in the 1906 comic “Dreams of the Rarebit Fiend” by Winsor McCay (1867-1934) in the New York (NY) Evening Telegram.
 
“What do you get when you cross a chili pepper, a shovel and a terrier?”/“A hot-diggity-dog” is a popular riddle.
 
   
Wikipedia: Hickory Dickory Dock
Hickory Dickory Dock is a children’s nursery rhyme, also sometimes called Hickety Dickety Dock
 
Hickory Dickory Dock
The mouse ran up the clock
The clock struck one
The mouse ran down (or “and down he run”, or “down the mouse ran”, or “The mouse was gone”)
Hickory Dickory Dock
 
Wikipedia: Dreams of a Rarebit Fiend
Dreams of a Rarebit Fiend was a newspaper comic strip written and drawn by Winsor McCay beginning in 1904. It was McCay’s second successful newspaper strip, after Little Sammy Sneeze secured him a position on the cartoon staff of the New York Herald newspaper. Rarebit Fiend was published in the Evening Telegram newspaper, which was published by the Herald at the time. The editor of the Herald required McCay to use a pseudonym for his work in the Telegram to keep it separate from his Herald strips, so McCay signed all of his Rarebit strips as “Silas”, borrowing the name of a neighborhood garbage cart driver.
 
McCay intended his Rarebit Fiend strip to be an amusing morality play, meant to comment on the dangers of overindulgence. It focuses on various people who have a passion for various foods - often, but not always, Welsh rarebit. Each strip features a different protagonist known as a Rarebit Fiend (who is rarely named in the comic strip, and who changes from strip to strip) in the course of strange dreams and nightmares. Upon awakening, the protagonist blames his dreams on eating the rarebit, or whatever other food he ate, thus exacting the price for their folly.
 
(Historical Dictionary of American Slang)
hot diggety [dog] interj. (used to express excitement or enthusiasm). Also vars.
1923 T.A. Dorgan, in Zwilling

46: Hot diggerty dog.
1922-24 McIntyre White Light 103: Hot diggedy dog!
1924 Dialect Notes v 270: Hot diggity.
1927 Benchley Early Worm 142: Hot dickety-dog!
1933 Benchley Chips 102: Hot dickety! It must be fun to have a horn.
1942 Oppenheimer & Houser Yank at Eton (film): Hot diggety dog!
1991 Bill & Ted’s Adventures (CBS-TV): Oh boy! Wow! Hot diggety dog!
 
20 September 1906, New York (NY) Evening Telegram, “Dreams of the Rarebit Fiend, by Silas” comic (by Winsor McCay) pg. 6, cols. 3-5:
PANEL ONE:
MOTHER TO BARRETT:  BARRETT! I WANT YOU! I WANT YOU TO TRY ON A NEW PAIR OF TROUSERS I’VE BOUGHT FOR YOU. COME IN!
 
PANEL TWO:
MOTHER:  MERCY! YOU’RE AS TALL AS PAPA. WELL, THEY FIT ALL RIGHT AND YOU MUST WEAR THEM, YOU ARE TOO BIG TO WEAR SHORT PANTS.
 
PANEL THREE:
MOTHER:  NOW, GO TO SCHOOL, BARRETT. AND BE A LITTLE GENTLEMAN, FOR YOU ARE A YOUNG MAN AND NOT A BOY. DO YOU UNDERSTAND?
 
PANEL FOUR:
(Pants and legs starts growing in the next five panels.  The other children at school are amazed—ed.)
BARRETT:  HOD DIGGETTY. THEY’RE SWELL! HOT DOG! JUST THE THING!  EH. THEY FEEL GREAT!  HOT DIGGETTY! WHEE!
 
PANEL FIVE:
BARRETT:  OF COURSE THEY MAKE A FELLOW FEEL AND LOOK TALLER BUT I WILL GET USED TO IT, I SUPPOSE.
 
PANEL SIX:
BARRETT:  GRACIOUS! BUT DON’T THEY LOOK LONG! I FEEL LIKE A SKY-SCRAPPER! I WISH I WAS NOT GOING TO SCHOOL TODAY. I DON’T FEEL RIGHT!
 
PANEL SEVEN:
BARRETT:  I WONDER IF MY MOTHER HAS PUT THESE—AH EH—I WONDER IF SHE KNOWS ANYTHING ABOUT,—AH—WHY, I BELIEVE I’LL GO HOME AND EXPLAIN IT ALL TO HER.
 
PANEL EIGHT:
BARRETT:  YES.  I DON’T WANT TO GO TO SCHOOL.  THIS FIRST DAY ANYWAY.  I FEEL SO QUEER.  I’LL ASK HER IF I CAN’T STAY HOME.
 
PANEL NINE:
(In school, looking normal—ed.)
TEACHER:  BARRETT McKEE! WERE YOUR EYES CLOSED? WERE YOU ASLEEP? I AM SURPRISED!
BARRETT:  I COULDN’T HELP IT, TEACHER. I ATE SOME TOASTED CHEESE WITH MY LUNCH TODAY.
   
4 June 1913, Fort Wayne (IN) Sentinel, pg.  8?, col. 5:
GOES BACK HOME
WITH NEW SLANG
“Hod Dickety-Dog” is a
New One That Comes
from Indiana
IS MAKING A BIG HIT
 
(Boxed—ed.)
“BEST SELLERS” IN CITY SLANG
Indianapolis—“Hod dickety dog!”
Boston—“I should worry.”
San Francisco—“Are you jerry to the old jazz?”
Denver—“It’s mush to me.”
St. Louis—“Gazipe!”
New Orleans—“Make a little dodo!”
(End of box—ed.)
 
Milroy, Ind., June 4—George Stoner came back from his week’s visit to Indianapolis with some new bits of slang, which already have swept Rush and Shelby counties and are the most popular things known here since “The Banks of the Wabash” first saw the light.
   
“I suppose those city fellows kidded the life out of you, hey, George?” asked Henry Talliff, who met Stoner at the interurban station.
   
“Hod dickety dog,” said Stoner.
   
“What’s that?” asked Tolliff. “Didn’t they get any change out of you?”
   
“Didn’t you hear me say ‘hod dickety dog?” asked the traveler. “What’s the matter with you rubes, anyway.  Everybody who is anybody knows that that means I’m jerry; I’m hep; I connect. (Column six—ed.) When you try to kid a fellow and he says ‘hod dickety dog!’ that means that
the bunk bounces off of him. Are you next?”
   
“I get you,” said Tolliff thoughtfully.
   
“Lemme tell you something here: “Hod dickety dog will be all the rage in New York before winter.  All good slang, like everything else, comes from Indiana, and travels east, and this is going fast.  ‘Round the Stanton House there in Indianapolis there was a bunch of traveling men and they gave me a line on the correct slang in various parts of the country; it’s different in different
cities. F’rinstance, ‘I should worry’ has the call in almost every city. It’s especially popular in Boston, and in New York they don’t know anything else. It isn’t very old.  It’s a Jewish expression and was born about the same time as Talmud. A fellow who sells bunion (?—ed.) plasters for a Denver house was telling me that out his way, if a person doesn’t care about the subject
under discussion he says, “It’s mush to me.”
   
“Now, out in San Francisco the most popular word is ‘the old jazz.’ It means anything you may happen to want it to. There was a St. Louis man there who thought that he was real cute.  He was trying to kid me, and just to show him I was wise I said ‘Hod dickety-dog.’ ‘I see you’re there with the gazipe,’ he says. ‘Get it?”
   
“Hod dickety-dog,” said Tolliff nodding.
 
“Down in New Orleans they say ‘I think I’ll take a little dodo,’ meaning they’re going to hunt the hay or go to sleep.  I got a lot more that I’ll tell you some other time.”
   
“Getting into any gambling houses, George?” asked his friend.
   
Stoner winked.
   
“Lose much?”
   
“Me?  Hod dickety-dog.”
     
Google Books
The Potters:
An American Comedy
By Joseph Patrick McEvoy
Published by The Reilly & Lee Co.
1924
Pg. 165:
Hot diggity-dog.
       
12 January 1924, Danville (VA) Bee, pg. 7, col. 1:   
Hot diggity dog! 
 
Google Books 
The Skyrocket:
A New Novel
By Adela Rogers St. Johns
New York, NY:  Cosmopolitan Book Corp.
1925
Pg. 139:
“Hot diggety dog !” he said, as the girl on the screen rose from the Roman bath, like Venus fresh from the… 
 
11 November 1934, Dallas (TX) Morning News, “Little Stanley” comic, section II, pg. 22:
“HOT DICKETTY DAWG!”
 
23 June 1935, Dallas (TX) Morning News, “Toonerville FOlks” comic, section III, pg. 26:
“HOT DIGGETY DOG!”
     
Google Books
My Sister Eileen
By Ruth McKenney
New York, NY: Harcourt, Brace & World
1938
Pg. 105:
“Hot diggety dog,” Buster continued with enthusiasm, now that he could speak out loud.
 
Google Books
Thorofare
By Christopher Morley
New York, NY: Harcourt, Brace
1942
Pg. 447:
“You know I been wan tin’ to get a real hot-diggety job down on the Panama Canal.”
   
Google Books
Clash by Night
By Clifford Odets
New York, NY: Random House
1942
Pg. 160:
The men think, “Hot diggety-dog! Now we’re married — that settles that!”
 
OCLC WorldCat record
Current country hits. Vol. 4
by Lefty Frizzell; Carl Smith; Ray Price; Neal Burris; George Morgan
Type:  Musical LP : Country music; English
Publisher: [New York, N.Y.] : Columbia, [1949]
Material Type: Music
Document Type: Sound Recording
Notes: Country songs. Biographical notes on container.
Description: 1 sound disc : analog, 33 1/3 rpm ; 10 in.
Contents: Don’t stay away (till love grows cold) (Lefty Frizzell)—(When you feel like you’re in love) don’t just stand there (Carl Smith)—I’ve got to hurry, hurry, hurry (Ray Price)—There’s no reason (Neal Burris)—Almost (George Morgan)—Hot diggity dog (Little Jimmy Dickens)—It’s a lovely, lovely world (Carl Smith)—Sad singin’, slow ridin’ (Polly Possum & Joe Wolverton with the Dog Patch Boys). 
   
OCLC WorldCat record
Hot diggity : (dog ziggity boom)
by Al Hoffman; Dick Manning
Type:  Musical score : linkadnan
Publisher: New York : Roncom Music Co., ©1956.
   
YouTube
1956’s Perry Como ” Hot Diggity ( Dog Ziggity Boom ) “
linkadnan
October 07, 2008
 
OCLC WorldCat record
Hot diggety dawg
by Jules Verne; Betty Buckley; Big Feats! Entertainment (Firm)
Type:  VHS video : Juvenile audience; English
Publisher: [New York?] : Big Feats! Entertainment, 1995.