The term was in use in science fiction fandom no later than 1947, when it was used (spelled "ego boo") in a letter from Rick Sneary published in the letter column of Thrilling Wonder Stories.
Amazing Stories | Grand Theft Auto: Liberty City Stories | Seven Stories Press | Just So Stories | Startling Stories | Celebrity Ghost Stories | Common Threads: Stories from the Quilt | Women: Stories of Passion | The Sneetches and Other Stories | James May's Toy Stories | Grand Theft Auto: Vice City Stories | The Saxon Stories | Ted Scott Flying Stories | Star Stories | List of Dave and Morley stories | Five Summer Stories | Yodok Stories | Word Is Out: Stories of Some of Our Lives | The Keepsake Stories | The Home Song Stories | The Best American Short Stories | Strange Stories from a Chinese Studio | Star Science Fiction Stories No.3 | Seven Stories | Planet Stories | Our Stories Films | Nightmares and Dreamscapes: From the Stories of Stephen King | New Stories from the South | Lady Chatterly's Stories | Kitchen Stories |
Between 1930 and 1940, his stories were published in Amazing Stories, Argosy All-Story Weekly, Black Mask, Collier's, Detective Fiction Weekly, Detective Tales, Double Detective, The Illustrated Detective Magazine, Mystery, The Phantom Detective, The Shadow, Startling Stories, Street & Smith Mystery Reader, Street & Smith's Detective Story Magazine, Thrilling Detective, Unknown Worlds and Wonder Stories.