My story...

The "MPG" part is obvious, from my interest in fuel efficient cars.

I got my 1.0L Pontiac Firefly in 2005. I started a fuel-economy related website about it, and that's also when I started participating in other forums. But I knew most of the readers would be American, and wouldn't have a CLUE what a Firefly was (only in Canada did we get the Pontiac-badged version of the Chevy Metro).

So I picked "MetroMPG" instead of "FireflyL/100km" and having to constantly explain what a Firefly was. And what the Metric system is!