Where did the simile as big a school bus come from?

There's no single origin story for the simile "as big as a school bus." It's a common phrase that likely emerged organically over time for a few reasons:

* School buses are readily recognizable: They're large, yellow, and ubiquitous, especially in areas with school systems. This makes them a convenient point of reference for size comparisons.

* School buses are large: Their sheer size makes them a natural choice when describing something that's exceptionally large.

* School buses are a common sight: Most people have encountered school buses, making it easy to understand the scale being referenced.

In short, the simile "as big as a school bus" is simply a product of everyday language, reflecting the size and familiarity of school buses. It's a natural and intuitive comparison that has likely been used for many years, without a specific point of origin.