No one knows the origin of this phrase that started in the early 20th century. If it had started in the 1920s, when it was at its height of popularity, one might have thought it was a way to bid farewell to the year 1923. But both “23” and “skidoo” already existed as slang for getting out (or away) in a hurry. Speculation about the origin includes the California mining town of Skidoo that had 23 saloons; going to town to hit them all might have been done without wasting time. Another thought is that construction workers at the Flatiron Building on Manhattan's West 23rd Street used the phrase to signal each other that an attractive young woman was passing. But no one knows for sure.