It is also common in the Pacific Northwest (where Linus lives) and the Midwest. Basically places where you can't wear sandals all year round.

> It's a European thing.

Pff. Socks in sandals is basically considered a fashion-sin by most people. But I can only speak for my part of Europe.

It's a way to filter out those people who consider fashion important. ;-)

"Most people find it a fashion-sin", as in most people, including those who don't even care about Fashion.