Bus horns have been a staple of sound effect libraries for decades because large vehicles need a horn that can be heard over city noise. Online, the isolated blast became a reusable punchline detached from actual traffic footage. Unlike the exaggerated MLG air horn used for celebration edits, this one stays grounded in real vehicle sound. It spread through meme edits, gaming videos, and short-form comedy where creators needed an instant warning for something big, late, or in the way.