It's a brand that has told Supreme to take a hike and is almost as ugly as a pair of Crocs, but Birkenstocks are hip and happening and succeeding where other fashion brands are failing.

How did they do it?

Here's the CNBC story of how the Birkenstock brand became so hot.

Treat 'em mean, keep 'em keen - that seems to be their brand mantra.

All too often, brand managers are too overly keen to jump into bed with just about anyone. Birkenstock chose to be far more strategic in their marketing - selecting their suitors very carefully. The result is false scarcity and a hot, desirable anti-fashion brand.