What is a flat tire 1920 slang?

In 1920s slang, a "flat tire" referred not just to a deflated car tire, but also to someone who was dull, boring, or lacking in energy. It could describe a person who failed to impress or entertain, much like a flat tire fails to perform its function. The phrase was part of the vibrant and playful language of the Roaring Twenties, characterized by its clever and colorful expressions.