“No biggie” means “no big deal.” A “biggie” is a “big deal,” something important.
 
“No real biggie” was said in 1973 by a narcotics agent, referring to marijuana in brownies. “No biggie” has been cited in print since at least 1974.
 
“Someone stole some of my rap CDs. Oh well, no biggie” is a joke on the saying.
 
 
Wiktionary: no biggie
Noun
no biggie (uncountable)
1. (idiomatic, slang) Not a big deal, not something to worry about.
       
Newspapers.com 
11 June 1973, Miami (FL) News, “Broward MD uses pot for eye patients” (UPI), pg. 3P, col. 7:
An agent for the U.S. Bureau of narcotics and Dangerous Drugs in Miami said he wasn’t concerned about Blanton’s case.
 
“Marijuana in brownies is no real biggie,” said the agent. “Sounds like a local problem to me.”
 
Newspapers.com
12 February 1974, Fort Lauderdale (FL) News, “Doctor Requests Return To Staff” by Barbara Lawry, pg. 2B, col. 8:
No criminal charges were filed. A Miami narcotics agent said at the time, “Marijuana in brownies is no real biggie.”
     
24 March 1974, Sunday Herald (Bellingham, WA), “You can’t keep a good man down…” by Bev Daniel, pg. 16, col. 2:
“I’ll have to give up hiking, but that’s no biggie.”
(Wayne Gerner.—ed.)
 
26 July 1974, Boston (MA) Globe, “Summer school: Student dollar days” by Teri Agins, pg. 31, col. 5:
But Harvard junior Jimmy Hill of Roxbury says that if you go there all the time, it’s really no biggie.
   
24 May 1977, Christian Science Monitor (Boston, MA), “Women CG cadets endure year: Changes made” by Mike Clancy (UPI), pg. 11, col. 3:
“The boys found out the girls could cry and it was no biggie,” said Miss Donner.
 
27 September 1977, Philadelphia (PA) Daily News, “TV Profile: Kristy McNichol” by Vernon Scott (UPI), pg. 35, col. 1:
“But it’s no biggie.”
(Kristy McNichol on not having a boyfriend.—ed.)
 
Google Books
Godchildren:
A Novel
By Charles Casey Martin
New York, NY: Viking
1990
Pg. 66:
“Commitments. Conflicts. Nobody’s perfect. Slipups’re bound to happen. Glad to help out. Anytime. No biggie, no biggie.”
 
Urban Dictionary
no biggie
not something to worry about.
shortened from the phrase “no big deal.”
If you can’t meet me Saturday, it’s no biggie.
by b00zar May 04, 2004
 
OCLC WorldCat record
It’s no biggie! : autism in the early childhood classroom
Author: Linda Barboa; Mary Lou Datema
Publisher: Hendersonville, TN : Goldminds Publishg, [2016] ©2016
Edition/Format:   Print book : Biography : English
 
OCLC WorldCat record
No biggy! : a story about overcoming everyday obstacles
Author: Elycia Rubin; Josh Talbot
Publisher: New York, New York : Rodale Kids, an imprint of Rodale Books, [2018] ©2018
Edition/Format:   Print book : Fiction : Preschool : English
Summary:
Getting frustrated is a part of life! And, whether Kiki is working on squeezing toothpaste right onto her toothbrush, getting the zipper to slide all the way up her jacket, or spreading cream cheese on a bagel, she learns that taking a deep breath, saying No Biggy! and trying again helps manage frustration.